Wireless communication system, wireless communication device, and communication method

ABSTRACT

A wireless communication system includes a server and a plurality of wireless communication devices representing nodes assigned to the server. The server sends notification information in which the starting position of a frame is specified. Each wireless communication device includes a notification information processing unit that receives notification information; and includes a communication processing unit that performs communication of the Time Division Duplex (TDD) type, and performs communication of the Carrier Sense Multiple Access (CSMA) type during the periods of time between downlink time period and uplink time period of the TDD type.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2017-126569, filed on Jun. 28,2017, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a wireless communicationsystem, a wireless communication device, and a wireless method.

BACKGROUND

In recent years, there has been a considerable rise in the use of theWi-Fi (Wireless Fidelity, registered trademark) in factories or openoffices. When the number of devices connected to the Wi-Fi increases,there are times when the line quality deteriorates due to radio waveinterference or hidden terminals.

For example, as a wireless communication system, the present-day Wi-Fiis operated based on a technology called the CSMA technology (CSMAstands for Carrier Sense Multiple Access). In the CSMA technology, eachwireless communication device (an access point or a device) performscommunication by monitoring the radio waves of other wirelesscommunication devices. Moreover, in the CSMA technology, before startingthe wireless communication, the concerned wireless communication deviceconfirms whether or not there is no wireless communication deviceperforming communication (i.e., carrier sense (CS)), and startscommunication when there is no wireless communication device performingcommunication (i.e., multiple access (MA)). Moreover, even afterbecoming able to perform communication as a result of the carrier sense(CS), the concerned wireless communication device further waits for arandom period of time before starting data transmission. However, in theCSMA technology, since control for communication authorization betweenaccess points and devices is used along with using standby period, thetraffic efficiency deteriorates rapidly if the number of devicesincreases.

In that regard, in order to resolve the issues arising in the CSMAtechnology, consider a case of operating the wireless communicationsystem in a technology called TDMA technology (TDMA stands for TimeDivision Multiple Access). For example, as far as communication of theTDMA type is concerned, the TDMA/TDD technology (TDD stands for TimeDivision Duplex) is implemented. Hereinafter, the TDMA/TDD technology iswritten as TDD technology.

In the TDD technology, a single channel is partitioned into time unitscalled slots along the time axis, and the data is sent and receivedwithin the periods of time decided in between the slots. For example, asillustrated in FIG. 47, a wireless communication system includes, aswireless communication devices, a gateway (hereinafter, abbreviated asGW), access points (hereinafter, abbreviated as APs), and a station(hereinafter, abbreviated as STA). Herein, downlink data is transferredin the path from the GW to the STA via APs #101 and #102, and uplinkdata is transferred in the opposite path. Moreover, in the TDDtechnology, downlink time periods are set in which downlink data istransferred (see “TDMA downlink” in FIG. 48), and uplink time periodsare set in which uplink data is transferred (see “TDMA uplink” in FIG.48). Conventional technique is described in Japanese Laid-open PatentPublication No. 2000-197089 and Japanese National Publication ofInternational Patent Application No. 2011-514740.

However, if the TDD technology is implemented in an environment formultihop communication having a multistage configuration, gap periodsare formed as follows.

For example, as illustrated in FIG. 48, during the transfer of downlinkdata, a delay period Δt101 attributed to the delay in slot units andattributed to the space propagation delay occurs between the GW and theAP #101. In an identical manner, delay periods Δt102 and Δt103attributed to the delay in slot units and attributed to the spacepropagation delay occur between the AP #101 and the AP #102 and betweenthe AP #102 and the STA, respectively. During the transfer of uplinkdata, it is the opposite to the case of downlink data transfer. In thiscase, at the time of performing downlink data transfer and uplink datatransfer between the GW and the STA; for example, after sending dataduring downlink time slots, the GW waits for a predetermined delayperiod (gap period) until data is received during uplink time slots.

SUMMARY

According to an aspect of an embodiment, a wireless communication systemincludes a server and a plurality of wireless communication devices. Theserver sends notification information in which starting position of aframe is specified. The plurality of wireless communication devicesrepresent nodes assigned to the server. Each of the plurality ofwireless communication devices includes a notification informationprocessing unit and a communication processing unit. The notificationinformation processing unit receives the notification information. Thecommunication processing unit, according to the notificationinformation, performs communication of time division duplex (TDD) type,and performs communication of carrier sense multiple access (CSMA) typeduring a period of time between a downlink time period and an uplinktime period of the TDD type.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for explaining the overview of a wirelesscommunication system according to a first embodiment;

FIG. 2 is a diagram for explaining transmission and reception of data inthe wireless communication system according to the first embodiment;

FIG. 3 is a block diagram illustrating an exemplary configuration of thewireless communication system according to the first embodiment;

FIG. 4 is a block diagram illustrating an exemplary configuration of aserver of the wireless communication system according to the firstembodiment;

FIG. 5 is a block diagram illustrating an exemplary configuration of agateway (GW) of the wireless communication system according to the firstembodiment;

FIG. 6 is a block diagram illustrating an exemplary configuration of anaccess point (AP) of the wireless communication system according to thefirst embodiment;

FIG. 7 is a block diagram illustrating an exemplary configuration of astation (STA) of the wireless communication system according to thefirst embodiment;

FIG. 8 is a block diagram illustrating an exemplary frame configurationin the wireless communication system according to the first embodiment;

FIG. 9 is a block diagram illustrating an exemplary configuration of atransmission-reception timing control unit of the GW, the APs, and theSTAs in the wireless communication system according to the firstembodiment;

FIG. 10 is a block diagram illustrating an exemplary configuration ofthe transmission-reception timing control unit of the GW, the APs, andthe STAs of the wireless communication system according to a secondembodiment;

FIG. 11 is a diagram for explaining the issues arising in the wirelesscommunication system according to the second embodiment;

FIG. 12 is a diagram for explaining an issue (1) arising in the wirelesscommunication system according to the second embodiment;

FIG. 13 is a diagram for explaining an issue (2) arising in the wirelesscommunication system according to the second embodiment;

FIGS. 14 and 15 are diagrams for explaining a solution to the issue (1)arising in the wireless communication system according to the secondembodiment;

FIG. 16 is a sequence diagram illustrating an exemplary solution to theissue (1) in the wireless communication system according to the secondembodiment;

FIGS. 17 and 18 are diagrams for explaining a solution to the issue (2)in the wireless communication system according to the second embodiment;

FIG. 19 is a sequence diagram illustrating an exemplary solution to theissue (2) in the wireless communication system according to the secondembodiment;

FIG. 20 is a diagram for explaining the solutions in the wirelesscommunication system according to the second embodiment;

FIGS. 21 to 23 are diagrams for explaining the issues arising in thewireless communication system according to a third embodiment;

FIG. 24 is a block diagram illustrating an exemplary configuration ofthe AP of the wireless communication system according to the thirdembodiment;

FIG. 25 is a diagram for explaining a solution to the issues arising inthe wireless communication system according to the third embodiment;

FIG. 26 is a sequence diagram illustrating an exemplary solution to theissues arising in the wireless communication system according to thethird embodiment;

FIG. 27 is an image diagram of delay measurement performed in thewireless communication system according to a fourth embodiment;

FIG. 28 is an image diagram of the transfer of a delay measurementpacket in the wireless communication system according to the fourthembodiment;

FIG. 29 is a block diagram illustrating an exemplary configuration ofthe GW in the wireless communication system according to the fourthembodiment;

FIG. 30 is a block diagram illustrating an exemplary configuration of adelay measuring unit of the GW in the wireless communication systemaccording to the fourth embodiment;

FIG. 31 is a diagram for explaining a solution to the issues arising inthe wireless communication system according to the fourth embodiment;

FIG. 32 is a sequence diagram illustrating an exemplary solution to theissues arising in the wireless communication system according to thefourth embodiment;

FIGS. 33 to 36 are diagrams for explaining the issues arising in thewireless communication system according to a fifth embodiment;

FIG. 37 is a diagram for explaining a solution 1-1 with respect to theissues arising in the wireless communication system according to thefifth embodiment;

FIG. 38 is a block diagram illustrating an exemplary configuration ofthe transmission-reception timing control unit of the GW, the APs, andthe STAs in the wireless communication system according to the fifthembodiment;

FIG. 39 is a sequence diagram illustrating an exemplary solution 1-1with respect to the issues arising in the wireless communication systemaccording to the fifth embodiment;

FIG. 40 is a diagram for explaining a solution 1-2 with respect to theissues arising in the wireless communication system according to thefifth embodiment;

FIG. 41 is a sequence diagram illustrating an exemplary solution 1-2with respect to the issues arising in the wireless communication systemaccording to the fifth embodiment;

FIG. 42 is a sequence diagram illustrating an exemplary solution 2 withrespect to the issues arising in the wireless communication systemaccording to the fifth embodiment;

FIG. 43 is a diagram illustrating an exemplary hardware configuration ofthe server;

FIG. 44 is a diagram illustrating an exemplary hardware configuration ofthe GW;

FIG. 45 is a diagram illustrating an exemplary hardware configuration ofthe AP;

FIG. 46 is a diagram illustrating an exemplary hardware configuration ofthe STA;

FIG. 47 is a diagram for explaining the overview of a conventionalwireless communication system; and

FIG. 48 is a diagram for explaining transmission and reception of datain the conventional wireless communication system.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be explained withreference to accompanying drawings. However, the technology disclosedherein is not limited by the embodiments described below.

[a] First Embodiment

Overview

FIG. 1 is a diagram for explaining the overview of a wirelesscommunication system according to a first embodiment. The wirelesscommunication system according to the first embodiment includes agateway 200 (hereinafter, written as a GW 200), a plurality of accesspoints 300 (hereinafter, written as APs 300), and a plurality ofstations (hereinafter, written as STAs 400). Herein, the GW 200, the APs300, and the STAs 400 represent examples of a “wireless communicationdevice”.

In the TDMA/TDD technology (TDMA stands for Time Division MultipleAccess, and TDD stands for Time Division Duplex), a single channel ispartitioned into time units called slots along the time axis, and thedata is sent and received within the periods of time decided in betweenthe slots. Hereinafter, the TDMA/TDD technology is written as TDDtechnology. FIG. 2 is a diagram for explaining transmission andreception of data in the wireless communication system according to thefirst embodiment. For example, downlink data is transferred in the pathfrom the GW 200 to the STA 400 via the two APs 300 (“AP #1” and “AP #2”in FIGS. 1 and 2), and uplink data is transferred in the opposite path.

Moreover, in the TDD technology, downlink time periods are set in whichdownlink data is transferred (see “TDMA downlink” in FIG. 2) and uplinktime periods are set in which uplink data is transferred (see “TDMAuplink” in FIG. 2). However, as described earlier, if the TDMA/TDDtechnology (hereinafter, written as TDD technology) is implemented in anenvironment for multihop communication having a multistageconfiguration, gap periods are formed due to delay periods (the delay inslot units and the space propagation delay) occurring at the time ofperforming data transfer using multihop communication. That is, in theTDD technology, at the time of performing downlink data transfer anduplink data transfer between the GW 200 and the STA 400; for example,after sending data during downlink time periods, the GW 200 waits for agap period until data is received during uplink time periods.

Herein, as illustrated in FIG. 2, in the wireless communication systemaccording to the first embodiment, communication of the CSMA type (CSMAstands for Carrier Sense Multiple Access) is assigned during the gapperiods. That is, in the wireless communication system according to thefirst embodiment, time periods of the CSMA type (“CSMA” illustrated inFIG. 2) are sandwiched between downlink time periods of the TDD type(“TDMA downlink” illustrated in FIG. 2) and uplink time periods of theTDD type (“TDMA uplink” illustrated in FIG. 2). The time periods of theCSMA type enable communication with the APs that are directly connectedwithout supporting data hopping, and can be used as control informationareas for data retransmission, connection monitoring, and radio wavemeasurement information.

For example, a server 100 specifies the starting positions of frames.According to the starting positions of the frames; the GW 200, the APs300, and the STAs 400 perform communication of the TDD type (“TDMAdownlink” and “TDMA uplink” illustrated in FIG. 2). Moreover, withrespect to the GW 200, the APs 300, and the STAs 400; communication ofthe CSMA type (“CSMA” illustrated in FIG. 2) is performed in the periodsof time (gap periods) between the downlink time periods and the uplinktime periods of the TDD type. In the GW 200, the APs 300, and the STAs400; the gap periods after downlink time periods of the TDD type and thegap periods after uplink time periods of the TDD type are measured anddecided in advance. According to the starting positions of the frames asspecified from the server 100; the GW 200, the APs 300, and the STAs 400perform communication of downlink data of the TDD type, performcommunication of the CSMA type, and perform communication of uplink dataof the TDD type. As a result, during the gap periods, it becomespossible to perform communication of the CSMA type between the GW 200and the AP 300, between the neighboring APs 300, and between the AP 300and the STA 400.

In this way, in the wireless communication system according to the firstembodiment, as a result of effectively using the gap periods,communication of the TDD type and communication of the CSMA type can beperformed in an efficient manner.

System Configuration

FIG. 3 is a block diagram illustrating an exemplary configuration of thewireless communication system according to the first embodiment. Thewireless communication system according to the first embodiment includesthe GW 200, a plurality of APs 300, a plurality of STAs 400, and theserver 100. Herein, the server 100 is connected to the GW 200 via awired line.

The server 100 performs monitoring control of the network and managesthe TDD slots. Moreover, the server 100 stores the data collected viathe network, and executes services in which the data is used. The GW 200is a device that joins a wireless Wi-Fi network and a wired line. TheAPs 300 are wireless Wi-Fi access points and perform data transfer. TheSTAs 400 are information terminals such as tablets, or are sensor nodes(cordless extension units) with respect to the GW 200 (a base unit).

Server 100

FIG. 4 is a block diagram illustrating an exemplary configuration of theserver 100 of the wireless communication system according to the firstembodiment. The server 100 includes a media processing layer 110, anapplication layer 120, and a database layer 130.

The media processing layer 110 includes a packet generating unit 111 anda packet extracting unit 112. The packet generating unit 111 generatespackets that include the data received from the application layer 120,and sends the packets to the GW 200 via the Ethernet and a router of thenetwork layer. The packet extracting unit 112 receives (extracts)packets from the network layer (the GW 200, the router, and theEthernet), and outputs them to the application layer 120.

For example, in the case in which the server 100 implements anauthentication service as a service, the application layer 120 includesan authenticating unit 121, and the database layer 130 includes anauthentication database 131 (hereinafter, written as authentication DB131). In this case, the authenticating unit 121 performs userauthentication by collating data (such as a user name and a password),which is sent to the server 100 from the STA 400 via the APs 300 and theGW 200, with the data stored in the authentication DB 131.

The application layer 120 includes a network monitoring unit 122(hereinafter, written as NW monitoring unit 122) and a network buildingunit 123 (hereinafter, written as NW building unit 123). The databaselayer 130 includes a monitoring log 132 indicating the records of avariety of data communication and includes configuration information 133indicating the arrangement relationship of the GW 200, the APs 300, andthe STAs 400. The NW monitoring unit 122 refers to the monitoring log132 to monitor a variety of data communication in the network. The NWbuilding unit 123 notifies the APs 300 and the STA 400 via the GW 200about the data containing the configuration information 133, andaccordingly performs network building and makes changes in the networkbuilding. That is, the GW 200, the APs 300, and the STAs 400 representnodes assigned to the server 100 according to the configurationinformation 133.

GW

FIG. 5 is a block diagram illustrating an exemplary configuration of theGW 200 of the wireless communication system according to the firstembodiment. The GW 200 includes an analog processing layer 210, a mediaprocessing layer 220, an operating system (0S)/driver layer 230, and anapplication layer 240. Herein, the analog processing layer 210, themedia processing layer 220, the OS/driver layer 230, and the applicationlayer 240 represent examples of a “notification information processingunit” of the GW 200.

The application layer 240 includes a user data processing unit 241 thatsends data, which is received from the OS/driver layer 230 (i.e.,information received from a wireless network), to the server 100 via theEthernet of the network layer. Moreover, the user data processing unit241 outputs data, which is received from the network layer (the server100 and the Ethernet), to the OS/driver layer 230.

The OS/driver layer 230 includes a transmission data buffer 231, atransmission data generating unit 232, a reception data buffer 233, anda reception data processing unit 234. The transmission data generatingunit 232 outputs data, which is received from the application layer 240,to the media processing layer 220 using the transmission data buffer231. The reception data processing unit 234 outputs the data, which isreceived by the reception data buffer 233 from the media processinglayer 220, to the application layer 240.

The media processing layer 220 includes a packet generating unit 221 anda packet extracting unit 222. The packet generating unit 221 generatespackets that include data received from the OS/driver layer 230, andoutputs the packets as signals to the analog processing layer 210. Thepacket extracting unit 222 extracts the packets from the signalsreceived from the analog processing layer 210, and outputs the packetsto the OS/driver layer 230.

The analog processing layer 210 includes an antenna 211, a modulatingunit 212, and a demodulating unit 213. The antenna 211 sends signals,which are received from the modulating unit 212, to the wireless network(the APs 300 and the STAs 400); and outputs signals, which are receivedfrom the wireless network (the APs 300 and the STAs 400), to thedemodulating unit 213. The modulating unit 212 modulates the signals,which are received from the media processing layer 220, and outputs themodulated signals to the antenna 211. The demodulating unit 213demodulates the signals, which are received by the antenna 211, andoutputs the demodulated signals to the media processing layer 220.

In this way, the GW 200 fulfils the role of a data bridge between awireless network and a wired network.

Moreover, in the GW 200, the application layer 240 further includes abeacon information processing unit 242 and a frame monitoring controlunit 243. The OS/driver layer 230 further includes atransmission-reception timing control unit 235. That is, the GW 200includes the beacon information processing unit 242, the framemonitoring control unit 243, and the transmission-reception timingcontrol unit 235 in addition to having the conventional functions.Herein, the beacon information processing unit 242, the frame monitoringcontrol unit 243, and the transmission-reception timing control unit 235represent examples of a “communication processing unit” of the GW 200.Regarding the beacon information processing unit 242, the framemonitoring control unit 243, and the transmission-reception timingcontrol unit 235; the explanation is given later.

AP

FIG. 6 is a block diagram illustrating an exemplary configuration of theAP 300 of the wireless communication system according to the firstembodiment. The AP 300 includes an analog processing layer 310, a mediaprocessing layer 320, an OS/driver layer 330, and an application layer340. Herein, the analog processing layer 310, the media processing layer320, the OS/driver layer 330, and the application layer 340 representexamples of a “notification information processing unit” of the AP 300.

The application layer 340 includes a user data processing unit 341 thatreceives data from the OS/driver layer 330 (i.e., information sent fromthe wireless network). Moreover, the user data processing unit 341outputs data to the OS/driver layer 330.

The OS/driver layer 330 includes a transmission data buffer 331, atransmission data generating unit 332, a reception data buffer 333, anda reception data processing unit 334. The transmission data generatingunit 332 outputs data, which is received from the application layer 340,to the media processing layer 320 using the transmission data buffer331. The reception data processing unit 334 outputs the data, which isreceived by the reception data buffer 333 from the media processinglayer 320, to the application layer 340.

The media processing layer 320 includes a packet generating unit 321 anda packet extracting unit 322. The packet generating unit 321 generatespackets that include data received from the OS/driver layer 330, andoutputs the packets as signals to the analog processing layer 310. Thepacket extracting unit 322 extracts the packets from the signalsreceived from the analog processing layer 310, and outputs the packetsto the OS/driver layer 330.

The analog processing layer 310 includes an antenna 311, a modulatingunit 312, and a demodulating unit 313. The antenna 311 sends signals,which are received from the modulating unit 312, to the wireless network(the GW 200, the APs 300, and the STAs 400); and outputs signals, whichare received from the wireless network (the GW 200, the APs 300, and theSTAs 400), to the demodulating unit 313. The modulating unit 312modulates the signals, which are received from the media processinglayer 320, and outputs the modulated signals to the antenna 311. Thedemodulating unit 313 demodulates the signals, which are received by theantenna 311, and outputs the demodulated signals to the media processinglayer 320.

In this way, the AP 300 fulfils the role of bridging data, which isreceived from the STAs 400, to the wired network; and fulfils the roleof bridging data to the other STAs 400 connected to the same AP 300.Moreover, in the first embodiment, the AP 300 is used as a multihopdevice. That is, the AP 300 fulfils the role of bridging information,which is received from the GW 200 or the AP 300 present in the upstreamside, to the AP 300 or the STA 400 present in the downstream side; andfulfils the role of bridging information, which is received from the AP300 or the STA 400 present in the downstream side, to the GW 200 or theAP 300 present in the upstream side.

Moreover, in the AP 300, the application layer 340 further includes abeacon information processing unit 342 and a frame monitoring controlunit 343. The OS/driver layer 330 further includes atransmission-reception timing control unit 335. That is, the AP 300includes the beacon information processing unit 342, the framemonitoring control unit 343, and the transmission-reception timingcontrol unit 335 in addition to having the conventional functions.Herein, the beacon information processing unit 342, the frame monitoringcontrol unit 343, and the transmission-reception timing control unit 335represent examples of a “communication processing unit” of the AP 300.Regarding the beacon information processing unit 342, the framemonitoring control unit 343, and the transmission-reception timingcontrol unit 335; the explanation is given later.

STA

FIG. 7 is a block diagram illustrating an exemplary configuration of theSTA 400 of the wireless communication system according to the firstembodiment. The STA 400 includes an analog processing layer 410, a mediaprocessing layer 420, an OS/driver layer 430, an application layer 440,and an interface layer. Herein, the analog processing layer 410, themedia processing layer 420, the OS/driver layer 430, and the applicationlayer 440 represent examples of a “notification information processingunit” of the STA 400.

The interface layer includes sensors, output devices, and input devices.The output devices include a display device and a speaker. The inputdevices include a switch, such as a keyboard, and a microphone. Thesensors, the output devices, and the input devices are connected to theapplication layer 440 via an external interface.

The application layer 440 includes a user data processing unit 441 thatoutputs data, which is received from the OS/driver layer 430 (i.e.,information received from the wireless network), to the interface layer.Moreover, the user data processing unit 441 outputs data, which isreceived from the interface layer (i.e., information received from thesensors or information received from the input devices), to theOS/driver layer 430.

The OS/driver layer 430 includes a transmission data buffer 431, atransmission data generating unit 432, a reception data buffer 433, anda reception data processing unit 434. The transmission data generatingunit 432 outputs data, which is received from the application layer 440,to the media processing layer 420 using the transmission data buffer431. The reception data processing unit 434 outputs data, which isreceived by the reception data buffer 433, from the media processinglayer 420 to the application layer 440.

The media processing layer 420 includes a packet generating unit 421 anda packet extracting unit 422. The packet generating unit 421 generatespackets that include data received from the OS/driver layer 430, andoutputs the packets as signals to the analog processing layer 410. Thepacket extracting unit 422 extracts the packets from the signalsreceived from the analog processing layer 410, and outputs the packetsto the OS/driver layer 430.

The analog processing layer 410 includes an antenna 411, a modulatingunit 412, and a demodulating unit 413. The antenna 411 sends signals,which are received from the modulating unit 412, to the wireless network(the GW 200 and the APs 300); and outputs signals, which are receivedfrom the wireless network (the GW 200 and the APs 300), to thedemodulating unit 413. The modulating unit 412 modulates the signalsreceived from the media processing layer 420, and outputs the modulatedsignals to the antenna 411. The demodulating unit 413 demodulates thesignals received by the antenna 411, and outputs the demodulated signalsto the media processing layer 420.

In this way, the STA 400 fulfils the role of sending information, whichis received from the sensors and the input devices, to the wirelessnetwork; and fulfils the role of outputting information, which isreceived from the wireless network, to the output devices.

Moreover, in the STA 400, the application layer 440 further includes abeacon information processing unit 442 and a frame monitoring controlunit 443. The OS/driver layer 430 further includes atransmission-reception timing control unit 435. That is, the STA 400includes the beacon information processing unit 442, the framemonitoring control unit 443, and the transmission-reception timingcontrol unit 435 in addition to having the conventional functions.Herein, the beacon information processing unit 442, the frame monitoringcontrol unit 443, and the transmission-reception timing control unit 435represent examples of a “communication processing unit” of the STA 400.Regarding the beacon information processing unit 442, the framemonitoring control unit 443, and the transmission-reception timingcontrol unit 435; the explanation is given later.

Example of Frame Configuration

Given below is the explanation of an exemplary frame configuration forenabling efficient communication of the TDD type and enabling efficientcommunication of the CSMA type.

FIG. 8 is a block diagram illustrating an exemplary frame configurationin the wireless communication system according to the first embodiment.In FIG. 8, “HYPER_FRAME #0” is a hyper frame representing the unit atwhich an arbitrary slot assignment can be done, and illustrates anexample of a single hyper frame. Moreover, in FIG. 8, “FRAME #0”, “FRAME#1”, . . . , “FRAME #9” are frames representing the unit for sendingbeacon information (notification information), and illustrate an exampleof the frames assigned to a single hyper frame. Furthermore, in FIG. 8,“SLOT #0”, “SLOT #1”, . . . , “SLOT #9” are slots representing thesmallest unit at which TDMA assignment or CSMA assignment is specified,and illustrate an example of the slots assigned to a single frame.

In the example illustrated in FIG. 8, in the hyper frame (1 second), 100slots can be assigned at the unit of 10 milliseconds. The server 100delivers the assignment of the communication method as beaconinformation to the entire network. The beacon information is once sentin the vicinity of the start of a frame (100 milliseconds). For example,the beacon information is assigned to the first slot (“SLOT #0”) among aplurality of slots (“SLOT #0”, “SLOT #1”, . . . , “SLOT #9”) assigned toa single frame. Then, since the information related to slot assignmentis included in the first slot, as far as changing slot assignment of theentire network is concerned, the setting can be changed at the unit of100 milliseconds at the minimum.

Method for Recognizing Starting Position of Frame

Given below is the explanation of a transmission-reception timingcontrol unit meant for recognizing the starting position of a frame.FIG. 9 is a block diagram illustrating an exemplary configuration of atransmission-reception timing control unit 35 of the GW 200, the APs300, and the STAs 400 in the wireless communication system according tothe first embodiment.

With reference to FIG. 9, the transmission-reception timing control unit35 is equivalent to the transmission-reception timing control unit 235of the GW 200, the transmission-reception timing control unit 335 of theAP 300, and the transmission-reception timing control unit 435 of theSTA 400. Moreover, with reference to FIG. 9, a beacon informationprocessing unit 42 is equivalent to the beacon information processingunit 242 of the GW 200, the beacon information processing unit 342 ofthe AP 300, and the beacon information processing unit 442 of the STA400. Furthermore, with reference to FIG. 9, a frame monitoring controlunit 43 is equivalent to the frame monitoring control unit 243 of the GW200, the frame monitoring control unit 343 of the AP 300, and the framemonitoring control unit 443 of the STA 400.

In an identical manner, with reference to FIG. 9, a packet extractingunit 22 is equivalent to the packet extracting unit 22 of the GW 200,the packet extracting unit 322 of the AP 300, and the packet extractingunit a of the STA 400. Moreover, with reference FIG. 9, a transmissiondata buffer 31 is equivalent to the transmission data buffer 231 of theGW 200, the transmission data buffer 331 of the AP 300, and thetransmission data buffer 431 of the STA 400. Furthermore, with referenceto FIG. 9, a reception data buffer 33 is equivalent to the receptiondata buffer 233 of the GW 200, the reception data buffer 333 of the AP300, and the reception data buffer 433 of the STA 400. Moreover, withreference to FIG. 9, a reception data processing unit 34 is equivalentto the reception data processing unit 234 of the GW 200, the receptiondata processing unit 334 of the AP 300, and the reception dataprocessing unit 434 of the STA 400.

As illustrated in FIG. 9, the transmission-reception timing control unit35 operates according to a free-running clock 30 installed therein. Thetransmission-reception timing control unit 35 includes a counter capture3501, a counter clear timing generating unit 3502, a counter 3503, and atransmission-reception timing deciding unit 3504.

Firstly, when all packets that include beacon information are detected(extracted), the packet extracting unit 22 sends a capture trigger tothe counter capture 3501 of the transmission-reception timing controlunit 35. The counter capture 3501 sets, as the beacon reception timing,the timing of receiving the capture trigger from the packet extractingunit 22. Then, the reception data processing unit 34 receives thepackets from the packet extracting unit 22 via the reception data buffer33; recognizes that the packets include beacon information; and notifiesthe beacon information processing unit 42 about the beacon information.The beacon information contains a slot number, a frame number, and anin-slot delay period representing the delay in slot units. Then, thebeacon information processing unit 42 notifies the counter clear timinggenerating unit 3502 about the beacon information (the slot number, theframe number, and the in-slot delay period).

The counter clear timing generating unit 3502 calculates the hyper framestarting timing based on the beacon reception timing received from thecounter capture 3501 and based on the beacon information (the slotnumber, the frame number, and the in-slot delay period) received fromthe beacon information processing unit 42. Herein, N_(SLOT) representsthe slot number; the slot duration is set to 10 [msec]; N_(FRAME)represents the frame number; the frame duration is set to 100 [msec];and Δt represents the in-slot delay time. Moreover, if T_(Beacon)represents the beacon reception timing and if T_(HYPER) _(_) _(FRAME)represents the hyper frame starting timing, then the hyper framestarting timing T_(HYPER) _(_) _(FRAME) is calculated using thefollowing equation.

T_(HYPER _ FRAME) = T_(Beacon) − N_(SLOT) × 10 [m sec ] − N_(FRAME) × 100  [m sec ] − Δ t

At the timing of calculation of the hyper frame starting timing, thecounter clear timing generating unit 3502 clears the counter value ofthe counter 3503. As a result, the transmission-reception timingdeciding unit 3504 becomes able to recognize the position of the countervalue “0” of the counter 3503. Moreover, since thetransmission-reception timing deciding unit 3504 becomes able torecognize the position of the counter value “0” of the counter 3503, theframe monitoring control unit 43 becomes able to recognize the start ofthe frame. According to the recognized counter value and according tothe start of the frame as recognized by the frame monitoring controlunit 43, the transmission-reception timing deciding unit 3504 decides onthe transmission-reception timing of the slots and the frames. Then, thetransmission-reception timing deciding unit 3504 notifies the packetextracting unit 22 and the transmission data buffer 31 about enablecontrol information indicating the decided transmission-receptiontiming, and thus assigns the time periods of the TDD type (“TDMAdownlink” and “TDMA uplink” illustrated in FIG. 2).

Moreover, the transmission-reception timing deciding unit 3504 assignsthe time periods of the CSMA type (“CSMA” illustrated in FIG. 2) betweenthe downlink time periods of the TDD type (“TDMA downlink” illustratedin FIG. 2) and the uplink time periods of the TDD type (“TDMA uplink”illustrated in FIG. 2). That is, the transmission-reception timingdeciding unit 3504 assigns the time periods of the CSMA type during thegap periods.

Specific Example

Explained below with reference to FIG. 2 are the operations performed inthe wireless communication system according to the first embodiment.

For example, the GW 200 receives, from the server 100, beaconinformation in which the starting position of frame is specified. Then,based on the beacon information and the beacon reception timing at whichthe beacon information is received, the GW 200 calculates the hyperframe starting timing. According to the calculated hyper frame startingtiming, the GW 200 assigns the hyper frame therein. That is, the GW 200assigns the time periods of the TDD type (“TDMA downlink” and “TDMAuplink” illustrated in FIG. 2), and assigns the time periods of the CSMAtype (“CSMA” illustrated in FIG. 2) during the periods of time that arepresent between the time periods of the TDD type and that representpredetermined gap periods. Moreover, in the frame, the GW 200 sends thebeacon information in the time period of the slot “SLOT #0”.

The AP 300 identified as “AP #1” and representing the neighboring nodeto the GW 200 receives the beacon information that is sent in the timeperiod of the slot “SLOT #0” from the GW 200. Then, based on the beaconinformation and the beacon reception timing at which the beaconinformation is received, the AP 300 identified as “AP #1” calculates thehyper frame starting timing. According to the calculated hyper framestarting timing, the AP 300 identified as “AP #1” assigns the hyperframe therein. That is, the AP 300 identified as “AP #1” assigns thetime periods of the TDD type (“TDMA downlink” and “TDMA uplink”illustrated in FIG. 2), and assigns the time periods of the CSMA type(“CSMA” illustrated in FIG. 2) during the periods of time that arepresent between the time periods of the TDD type and that representpredetermined gap periods. Herein, the downlink time periods of the TDDtype (“TDMA downlink” illustrated in FIG. 2) as assigned to the AP 300identified as “AP #1” are delayed with respect to the downlink timeperiods of the TDD type (“TDMA downlink” illustrated in FIG. 2) asassigned to the GW 200. Moreover, the uplink time periods of the TDDtype (“TDMA uplink” illustrated in FIG. 2) as assigned to the GW 200 aredelayed with respect to the uplink time periods of the TDD type (“TDMAuplink” illustrated in FIG. 2) as assigned to the AP 300 identified as“AP #1”. In the concerned frame, the AP 300 identified as “AP #1” sendsbeacon information in the time period of the slot “SLOT #0”.

The AP 300 identified as “AP #2” and representing the neighboring nodeto the AP 300 “identified as “AP #1” receives beacon information sent inthe time period of the slot “SLOT #0” from the AP 300 identified as “AP#1”. Then, based on the beacon information and the beacon receptiontiming at which the beacon information is received, the AP 300identified as “AP #2” calculates the hyper frame starting timing.According to the calculating hyper frame starting timing, the AP 300identified as “AP #2” assigns the hyper frame therein. That is, the AP300 identified as “AP #2” assigns the time periods of the TDD type(“TDMA downlink” and “TDMA uplink” illustrated in FIG. 2), and assignsthe time periods of the CSMA type (“CSMA” illustrated in FIG. 2) duringthe periods of time that are present between the time periods of the TDDtype and that represent predetermined gap periods. Herein, the downlinktime periods of the TDD type (“TDMA downlink” illustrated in FIG. 2) asassigned to the AP 300 identified as “AP #2” are delayed with respect tothe downlink time periods of the TDD type (“TDMA downlink” illustratedin FIG. 2) as assigned to the AP 300 identified as “AP #1”. Moreover,the uplink time periods of the TDD type (“TDMA uplink” illustrated inFIG. 2) as assigned to the AP 300 identified as “AP #1” are delayed withrespect to the uplink time periods of the TDD type (“TDMA uplink”illustrated in FIG. 2) as assigned to the AP 300 identified as “AP #2”.In the concerned frame, the AP 300 identified as “AP #2” sends beaconinformation in the time period of the slot “SLOT #0”.

The STA 400 that represents the neighboring node to the AP 300identified as “AP #2” receives the beacon information sent in the timeperiod of the slot “SLOT #0” from the AP 300 identified as “AP #2”.Then, based on the beacon information and the beacon reception timing atwhich the beacon information is received, the STA 400 calculates thehyper frame starting timing. According to the calculated hyper framestarting timing, the STA 400 assigns the hyper frame therein. That is,the STA 400 assigns the time periods of the TDD type (“TDMA downlink”and “TDMA uplink” illustrated in FIG. 2), and assigns the time periodsof the CSMA type (“CSMA” illustrated in FIG. 2) during the periods oftime that are present between the time periods of the TDD type and thatrepresent predetermined gap periods. Herein, the downlink time periodsof the TDD type (“TDMA downlink” illustrated in FIG. 2) as assigned tothe STA 400 are delayed with respect to the downlink time periods of theTDD type (“TDMA downlink” illustrated in FIG. 2) as assigned to the AP300 identified as “AP #2”. Moreover, the uplink time periods of the TDDtype (“TDMA uplink” illustrated in FIG. 2) as assigned to the AP 300identified as “AP #2” are delayed with respect to the uplink timeperiods of the TDD type (“TDMA uplink” illustrated in FIG. 2) asassigned to the STA 400.

Effect

As described above, the wireless communication system according to thefirst embodiment includes the server 100 and includes a plurality ofwireless communication devices (the GW 200, the APs 300, and the STAs400) representing the nodes assigned to the server 100. The server 100sends notification information (beacon information) in which thestarting positions of frames are specified. Each of a plurality ofwireless communication devices includes a notification informationprocessing unit and a communication processing unit.

The notification information processing unit receives the beaconinformation. For example, when the GW 200 represents the wirelesscommunication device, the notification information processing unitincludes the analog processing layer 210, the media processing layer220, the OS/driver layer 230, and the application layer 240.Alternatively, when the AP 300 represents the wireless communicationdevice, the notification information processing unit includes the analogprocessing layer, the media processing layer 320, the OS/driver layer330, and the application layer 340. Still alternatively, for example,when the STA 400 represents the wireless communication device, thenotification information processing unit includes the analog processinglayer 410, the media processing layer 420, the OS/driver layer 430, andthe application layer 440.

According to the beacon information, the communication processing unitperforms communication of the TDD type, and performs communication ofthe CSMA type during the periods of time between the downlink timeperiods and the uplink time periods of the TDD type. For example, whenthe GW 200 represents the wireless communication device, thecommunication processing unit includes the transmission-reception timingcontrol unit 235, the beacon information processing unit 242, and theframe monitoring control unit 243. Alternatively, for example, when theAP 300 represents the wireless communication device, the communicationprocessing unit includes the transmission-reception timing control unit335, the beacon information processing unit 342, and the framemonitoring control unit 343. Still alternatively, when the STA 400represents the wireless communication device, the communicationprocessing unit includes the transmission-reception timing control unit435, the beacon information processing unit 442, and the framemonitoring control unit 443.

In this way, in the wireless communication system according to the firstembodiment, the server 100 sends beacon information; and the GW 200, theAPs 300, and the STAs 400 perform communication of the TDD type andperform communication of the CSMA type during the gap periods accordingto the beacon information. As a result, during the gap periods,communication of the CSMA type can be performed between the GW 200 andthe AP 300, between the neighboring APs 300, and between the AP 300 andthe STA 400. Thus, in the wireless communication system according to thefirst embodiment, the gap periods are used in an effective manner,thereby enabling efficient communication of the TDD type and efficientcommunication of the CSMA type.

[b] Second Embodiment

FIG. 10 is a block diagram illustrating an exemplary configuration ofthe transmission-reception timing control unit 35 of the GW 200, the APs300, and the STAs 400 of the wireless communication system according toa second embodiment. The transmission-reception timing control unit 35includes a switching path counter 3505 in addition to having theconfiguration illustrated in FIG. 9.

Issues

As one of the features of multihop communication, path switching isknown in which, when the AP 300 malfunctions thereby resulting in astate in which data communication is not normally performed between theGW 200 and the STA 400, data is sent using another path. As a result ofperforming path switching, it becomes possible to enhance the dataarrival factor between the GW 200 and the STA 400. Thus, path switchingis given importance in factories in which a large volume of data iscommunicated or in the Internet of Things (IoT) technology.

FIG. 11 is a diagram for explaining the issues arising in the wirelesscommunication system according to the second embodiment. For example, ina path P21, beacon information #0 (“Beacon #0” illustrated in FIG. 11)is sent from the GW 200 to the STA 400. In a path P22, the beaconinformation #0 is sent from the GW 200 to the AP 300 (identified as “AP#1” illustrated in FIG. 11), and beacon information #1 (“Beacon #1”illustrated in FIG. 11) is sent from the AP 300 identified as “AP #1” tothe STA 400.

In this case, in order to perform path switching at a faster pace duringmultihop communication, it is desirable that control is performed toensure that both sets of beacon information are constantly receivable,and that the frame starting position is recognizable based on the beaconinformation in both paths (the communication path and the switchingpath). At the time of receiving the beacon information in thecommunication path, the transmission-reception timing control unit 35clears the counter value of the counter 3503 according to the framestarting position. On the other hand, when the beacon information in theswitching path is received, the transmission-reception timing controlunit 35 clears the counter value of the switching path counter 3505according to the frame starting position. The transmission-receptiontiming control unit 35 includes the switching path counter 3505. Hence,when path switching is performed, the counter value of the switchingpath counter 3505 is loaded in the counter 3503 meant for framegeneration. As a result, the frame starting position can be changed in ashort period of time.

However, when the position of the beacon information is defined to bethe starting criterion as is the case in a normal Wi-Fi system, in thecase of performing multihop communication, it is sometimes difficult forthe STA 400 to receive both sets of beacon information due to issues (1)and (2) given below.

Issue (1)

FIG. 12 is a diagram for explaining the issue (1) arising in thewireless communication system according to the second embodiment. Withreference to FIG. 12, the GW 200 and the AP 300 use the same channel. Inthis case, when the GW 200 and the AP 300 send beacon information at theframe starting position, the sets of beacon information sent from the GW200 and the AP 300 interfere in the STA 400. That is, there occurs apacket reception trouble attributed to radio wave interference. In thiscase, there is a possibility that the STA 400 does not receive thebeacon information.

Issue (2)

FIG. 13 is a diagram for explaining the issue (2) arising in thewireless communication system according to the second embodiment. Withreference to FIG. 13, the GW 200 and the AP 300 use different channels.In this case, the number of channels receivable by the STA 400 in oneinstance (that is, at the same timing) is one. Hence, the STA 400 canreceive any one set of beacon information (for example, the beaconinformation sent from the GW 200) but does not receive the other set ofbeacon information (for example, the beacon information sent from the AP300).

Solution

In the wireless communication system according to the second embodiment,the positions of the slots in which the beacon information sent from theGW 200 and the AP 300 is assigned are shifted. For example, in aparticular frame, a nod hop count indicating the involved node count isset; and, at the time of receiving or transferring the beaconinformation, the node hop count is incremented by one. In a plurality ofpaths P21 and P22 meant for transferring the beacon information, the GW200 and the AP 300 assign beacon information to the slots present at thepositions corresponding to the node hop count among a plurality ofslots. With that, the abovementioned issues get resolved.

In a frame, the GW 200 sends beacon information in the time period ofthe slot “SLOT #0”. Moreover, the AP 300 uses the neighboring slotaccording to the node hop count (for example, uses the slot “SLOT #1”when the node hop count is one, and uses the slot “SLOT #2” when thenode hop count is two”). Moreover, in the time period of the slot inwhich the GW 200 and the neighboring AP 300 send beacon information, theGW 200 and the neighboring AP 300 switch to the standby state or thereception state and stop any transmission in the time period of thatslot.

Solution (1)

FIGS. 14 and 15 are diagrams for explaining a solution to the issue (1)arising in the wireless communication system according to the secondembodiment. FIG. 16 is a sequence diagram illustrating an exemplarysolution to the issue (1) in the wireless communication system accordingto the second embodiment. FIG. 20 is a diagram for explaining thesolutions in the wireless communication system according to the secondembodiment.

With reference to FIGS. 14 and 15, the GW 200 and the AP 300 use thesame channel.

In this case, with reference to FIGS. 14 and 20, the AP 300 representingthe neighboring node to the GW 200 switches to the reception state andstops all transmission (Step S100 illustrated in FIG. 16). At that time,in the concerned frame, the GW 200 sends beacon information in the timeperiod of the slot “SLOT #0” (Step S101 illustrated in FIG. 16). The AP300 representing the neighboring node of the GW 200 receives the beaconinformation sent from the GW 200 in the time period of the slot “SLOT#0” (Step S102 illustrated in FIG. 16). Moreover, the STA 400representing the neighboring node to the GW 200 and the AP 300 receivesthe beacon information sent from the GW 200 in the time period of theslot “SLOT #0” (Step S103 illustrated in FIG. 16).

Subsequently, with reference to FIGS. 15 and 20, the GW 200 switches tothe standby state after sending the beacon information in the timeperiod of the slot “SLOT #0”, and stops all transmission (Step S104illustrated in FIG. 16). At that time, the AP 300 representing theneighboring node to the GW 200 switches to the transmission-receptionstate to be able to perform transmission (Step S105 illustrated in FIG.16), and sends beacon information in the time period of the slot “SLOT#1” (Step S106 illustrated in FIG. 16). The STA 400 representing theneighboring node to the GW 200 and the AP 300 receives the beaconinformation sent from the AP 300 in the time period of the slot “SLOT#1” (Step S107 illustrated in FIG. 16).

In this way, even when the GW 200 and the AP 300 are using the samechannel, the beacon information sent from the GW 200 and the beaconinformation sent from the AP 300 have a sufficiently-offset timeinterval therebetween. Hence, in the wireless communication systemaccording to the second embodiment, the packets that include beaconinformation and that are sent from the GW 200 and the AP 300 do notinterfere (are not caught in radio wave interference), and the STA 400becomes able to receive the beacon information.

Solution (2)

FIGS. 17 and 18 are diagrams for explaining a solution to the issue (2)in the wireless communication system according to the second embodiment.FIG. 19 is a sequence diagram illustrating an exemplary solution to theissue (2) in the wireless communication system according to the secondembodiment.

With reference to FIGS. 17 and 18, the GW 200 and the AP 300 usedifferent channels.

In this case, with respect to FIGS. 17 and 20, the AP 300 representingthe neighboring node to the GW 200 switches to the channel for the GW200 (Step S200 illustrated in FIG. 19). In an identical manner, the STA400 representing the neighboring node to the GW 200 and the AP 300switches to the channel for the GW 200 (Step S201 illustrated in FIG.19). At that time, the GW 200 sends beacon information in the timeperiod of the slot “SLOT #0” (Step S202 illustrated in FIG. 19). The AP300 representing the neighboring node to the GW 200 receives the beaconinformation sent from the GW 200 in the time period of the slot “SLOT#0” (Step S203 illustrated in FIG. 19). Moreover, the STA 400representing the neighboring node to the GW 200 and the AP 300, receivesthe beacon information sent from the GW 200 in the time period of theslot “SLOT #0” (Step S204 illustrated in FIG. 19).

Subsequently, with reference to FIGS. 18 and 20, when the beaconinformation is received from the GW 200, the AP 300 representing theneighboring node to the GW 200 switches to the channel for the AP 300(Step S205 illustrated in FIG. 19). In an identical manner, when thebeacon information is received from the GW 200; the STA 400 representingthe neighboring node to the GW 200 and the AP 300 switches to thechannels for the AP 300 (Step S206 illustrated in FIG. 19). At thattime, the AP 300 representing the neighboring node to the GW 200 sendsbeacon information in the time period of the slot “SLOT #1” (Step S207illustrated in FIG. 19). The STA 400 representing the neighboring nodeto the GW 200 and the AP 300 receives the beacon information sent fromthe AP 300 in the time period of the slot “SLOT #1” (Step S208illustrated in FIG. 19).

In this way, even when the GW 200 and the AP 300 are using differentchannels, the beacon information sent from the GW 200 and the beaconinformation sent from the AP 300 have a sufficiently-offset timeinterval therebetween. Hence, in the wireless communication systemaccording to the second embodiment, a channel switching period can besecured in the STA 400, and the STA 400 becomes able to receive thebeacon information sent from the GW 200 and the beacon information sentfrom the AP 300.

As another advantage, the latest information in the beacon informationcan be sent in the same frame. The beacon information containsinformation meant for communicating the information from the GW 200without modification and contains information added in the APs 300. Inthe wireless communication system according to the second embodiment, atthe same timing, the beacon information from each AP 300 gets delayed byone frame. On the other hand, in the wireless communication systemaccording to the second embodiment, by shifting the position of thebeacon information by one slot at a time, the beacon informationreceived in the same frame can be sent without modification.

Effect

As described above, in the wireless communication system according tothe second embodiment, among a plurality of slots identified as “SLOT#0”, “SLOT #1”, . . . , “SLOT #9” assigned to a single frame, thenotification information (beacon information) is assigned to the firstslot “SLOT #0”. The notification information processing unit of aplurality of wireless communication devices (in this case, the GW 200and the AP 300) assigns, in a plurality of paths P21 and P22 in whichthe beacon information is transferred, the beacon information in theslots present at the positions corresponding to the node hop countindicating the involved node count.

For example, when the GW 200 represents the wireless communicationdevice, the notification information processing unit includes the analogprocessing layer 210, the media processing layer 220, the OS/driverlayer 230, and the application layer 240. In that case, the notificationinformation processing unit of the GW 200 (for example, thetransmission-reception timing control unit 235 of the OS/driver layer230) assigns, in the path P21, the beacon information in the slot “SLOT#0” that, among a plurality of slots, is present at the positioncorresponding to the node hop count of zero.

For example, when the AP 300 represents the wireless communicationdevice, the notification information processing unit includes the analogprocessing layer 310, the media processing layer 320, the OS/driverlayer 330, and the application layer 340. In this case, the notificationinformation processing unit of the AP 300 (for example, thetransmission-reception timing control unit 335 of the OS/driver layer330) assigns, in the path P22, the beacon information in the slot “SLOT#1” that, among a plurality of slots, is present at the positioncorresponding to the node hop count of one.

In this way, in the wireless communication system according to thesecond embodiment, as a result of shifting the position of the beaconinformation by one slot at a time, the STA 400 can receive the beaconinformation regardless of whether the same channel is used or differentchannels are used.

[c] Third Embodiment

In the wireless communication system according to the second embodiment,the position of the beacon information is shifted by one slot at a time.However, when a plurality of paths having the same node hop count ispresent, the following issues arise.

Issues

FIG. 21 is a diagram for explaining the issues arising in the wirelesscommunication system according to a third embodiment. For example, in apath P31, the beacon information #0 (“Beacon #0” illustrated in FIG. 21)is sent from the GW 200 to the first AP 300 (“AP #1” illustrated in FIG.21). Moreover, in the path P31, the beacon information #1 (“Beacon #1”illustrated in FIG. 21) is sent from the AP 300 identified as “AP #1” tothe STA 400. In a path P32, the beacon information #0 is sent from theGW 200 to the second AP 300 (“AP #2” illustrated in FIG. 21), and beaconinformation #2 (“Beacon #2” illustrated in FIG. 21) is sent from the AP300 identified as “AP #2” to the STA 400.

In this case, there arises an issue that it is difficult for the STA 400to receive the beacon information #1 and the beacon information #2 sentfrom the two APs identified as “AP #1” and “AP #2” having the same nodehop count. Herein, it is possible to think of a method in whichdifferent slots are used in all APs 300. However, when a large number ofAPs 300 are present, it results in deterioration of the trafficefficiency.

FIGS. 22 and 23 are diagrams for explaining the issues arising in thewireless communication system according to the third embodiment. Forexample, the beacon information #0 is sent from the GW 200 to the twoAPs 300 (identified as “AP #1” and “AP #2” illustrated in FIG. 22). Atthat time, the beacon information #1 is sent from the AP 300 identifiedas “AP #1” to the STA 400, and the beacon information #2 is sent fromthe AP 300 identified as “AP #2” to two STAs 400 (“STA #1” and “STA #2”illustrated in FIG. 22).

In this case, for example, it is possible to think of a method ofshifting the position of the slot to which the beacon information #2sent from the AP 300 (identified as “AP #2”) is assigned. However, thereexists the STA 400 identified as “STA #2” that receives the beaconinformation in the time period of the slot “SLOT #1”. That is, asillustrated in FIG. 23, since the STA 400 identified as “STA #1”receives the beacon information in the in-use channel in the path P31,it is difficult for the STA 400 to receive the beacon information in theswitching path (the path P32).

Solution

FIG. 24 is a block diagram illustrating an exemplary configuration ofthe AP 300 of the wireless communication system according to the thirdembodiment. In the AP 300 illustrated in FIG. 24, the OS/driver layer330 further includes a V beacon buffer 336 meant for storing the beaconinformation.

FIG. 25 is a diagram for explaining a solution to the issues arising inthe wireless communication system according to the third embodiment.Herein, with respect to the AP 300 identified as “AP #2” and the STA 400identified as “STA #1” in the path P32 among a plurality of paths P31and P32 having the same node hop count, the server 100 specifies theslot in which the copied beacon information is to be assigned.

In this case, in the AP 300 identified as “AP #1” in the path P31, thetransmission-reception timing control unit 335 of the OS/driver layer330 assigns the beacon information in the slot “SLOT #1” at the positioncorresponding to the node hop count of one among a plurality of slots.Then, the transmission-reception timing control unit 335 of theOS/driver layer 330 sends that beacon information from the transmissiondata buffer 331 to the STA 400, which represents the neighboring node tothe AP 300 identified as “AP #1”, via the media processing layer 320 andthe analog processing layer 310. In the path P31, the STA 400 identifiedas “STA #1” receives the beacon information sent in the time period ofthe slot “SLOT #1” from the AP 300 identified as “AP #1”.

On the other hand, in the AP 300 identified as “AP #2” in the path P32,the transmission-reception timing control unit 335 of the OS/driverlayer 330 copies the beacon information. Then, thetransmission-reception timing control unit 335 assigns V beaconinformation (the copied beacon information) in the slot “SLOT #1”present at the position specified by the server 100. Thetransmission-reception timing control unit 335 sends the V beaconinformation from the V beacon buffer 336 to the STA 400, whichrepresents the neighboring node to the AP 300 identified as “AP #2”, viathe media processing layer 320 and the analog processing layer 310. Inthe path P32, the STA 400 identified as “STA #1” receives the V beaconinformation sent in the time period of the slot “SLOT #N” from the AP300 identified as “AP #2”. With that, the abovementioned issues getresolved.

FIG. 26 is a sequence diagram illustrating an exemplary solution to theissues arising in the wireless communication system according to thethird embodiment.

When the paths P31 and P32 of the STA 400 identified as “STA #1” aredecided, the server 100 notifies the GW 200 about STA informationcontaining the used path, the switching path, and the V beacon slotinformation (Step S300). Herein, the used path implies the path P31 andthe switching path implies the path P32. The V beacon slot informationrepresents information for specifying, in the path P32, the slot towhich the V beacon information (the copied beacon information) is to beassigned.

The GW 200 receives the STA information from the server 100 and adds itto the beacon information #0. Then, the GW 200 sends the beaconinformation #0, which contains the STA information, in the time periodof the slot “SLOT #0” (Step S301).

In the path P31, the AP 300 identified as “AP #1” receives the beaconinformation #0 sent from the GW 200 in the time period of the slot “SLOT#0”. Then, the AP 300 identified as “AP #1” assigns the beaconinformation #0 to the slot “SLOT #1” present at the positioncorresponding to the node hop count of one among a plurality of slots.Subsequently, the AP 300 identified as “AP #1” sends the beaconinformation #0 as the beacon information #1 in the time period of theslot “SLOT #1” (Step S302).

In the path P32, the AP 300 identified as “AP #2” receives the beaconinformation #0 sent from the GW 200 in the time period of the slot “SLOT#0”. Then, the AP 300 identified as “AP #2” assigns the beaconinformation #0 to the slot “SLOT #1” present at the positioncorresponding to the node hop count of one among a plurality of slots.Subsequently, the AP 300 identified as “AP #2” sends the beaconinformation #0 as the beacon information #2 in the time period of theslot “SLOT #1”. Moreover, the AP 300 identified as “AP #2” copies thebeacon information #0 and stores it as V beacon information in a memory(not illustrated) (Step S303).

In the path P31, the STA 400 identified as “STA #1” receives the beaconinformation #1 that is sent in the time period of the slot “SLOT #1”from the AP 300 identified as “AP #1”. At that time, the STA 400identified as “STA #1” obtains the STA information included in thebeacon information #1 (Step S304).

In the path P32, the STA 400 identified as “STA #2” receives the beaconinformation #2 that is sent in the time period of the slot “SLOT #1”from the AP 300 identified as “AP #2” (Step S305).

Herein, in the path P31, it is difficult for the STA 400 to receive thebeacon information #2, which is sent in the time slot of the slot “SLOT#1” from the AP 300 identified as “AP #2”, because the channels aredifferent. In that regard, the STA 400 identified as “STA #1” changesthe channel based on the obtained STA information (Step S306).

The AP 300 identified as “AP #2” assigns the V beacon information (thecopied beacon information) to the slot “SLOT #N” present at the positionspecified by the server 100. Then, the AP 300 identified as “AP #2”sends the V beacon information (the copied beacon information) in thetime period of the slot “SLOT #N” (Step S307).

The STA 400 identified as “STA #1” receives the V beacon information(the copied beacon information) in the time period of the slot “SLOT #N”from the AP 300 identified as “AP #2” (Step S308).

Effect

As described above, in the wireless communication system according tothe third embodiment, there are times when a plurality of paths P31 andP32 having the same node hop count is present. In that regard, thenotification information processing unit of a plurality of wirelesscommunication devices (in this case, the APs 300) assigns, in the firstpath (the path P31), notification information (beacon information) tothe slot present at the position corresponding to the node hop count. Onthe other hand, the notification information processing unit of aplurality of wireless communication devices (in this case, the APs 300)assigns, in the other path (the path P32) other than the first path(other the path P31); copies the beacon information; and assigns thecopied beacon information to the slot present at the position specifiedby the server 100.

For example, when the AP 300 represents the wireless communicationdevice, the notification information processing unit includes the analogprocessing layer, the media processing layer 320, the OS/driver layer330, and the application layer 340. In this case, in the path P31, thenotification information processing unit of the AP 300 identified as “AP#1” (for example, the transmission-reception timing control unit 335 ofthe OS/driver layer 330) assigns the beacon information to the slot“SLOT #1” present at the position corresponding to the node hop count ofone among a plurality of slots. On the other hand, in the path P32, thenotification information processing unit of the AP 300 identified as “AP#2” (for example, the transmission-reception timing control unit 335)assigns the copied beacon information to the slot “SLOT #N” present atthe position specified by the server 100 among a plurality of slots.

In this way, in the wireless communication system according to the thirdembodiment, even when a plurality of paths P31 and P32 having the samenode hop count is present, the STA 400 identified as “STA #1” canreceive the beacon information from the APs 300 identified as “AP #1”and “AP #2”.

[d] Fourth Embodiment

Correction of Transmission Start Position of Uplink Data of TDD Type

In order for the GW 200, the AP 300, and the STA 400 to receive uplinkdata in the time periods of the TDD type, the AP 300 and the STA 400need to match the transmission start position of the uplink data of theTDD type. For example, the GW 200 measures the delay period when data issent and received in the path from the GW 200 to the STA 400; and, basedon the delay period, the STA 400 adjusts the timing for sending datausing multihop communication of the TDD type. In the followingexplanation, measuring the delay period is written as delay measurement,and adjusting the timing based on the delay period is written as delayadjustment.

FIG. 27 is a conceptual diagram of delay measurement performed in thewireless communication system according to a fourth embodiment. Forexample, downlink data is transferred in the path from the GW 200 to theSTA 400 via the AP 300 (“AP #1” illustrated in FIG. 27), and uplink datais transferred in the opposite path. As illustrated in FIG. 27, theadvancement amount (the advancement period) is used for adjusting thetiming of sending the data using multihop communication of the TDD type,and the time periods of the CSMA type are used for measuring theadvancement amount. Upon receiving the beacon information, at the pointof time of finalization of the frame position, the STA 400 issues aprobe request (a connection request) to the GW 200 in the time periodsof the CSMA type. In response to the probe request, the GW 200 sendsback a probe response (a connection request response).

Given below is the explanation of a delay measurement packet. FIG. 28 isa conceptual diagram of the transfer of a delay measurement packet inthe wireless communication system according to the fourth embodiment.FIG. 29 is a block diagram illustrating an exemplary configuration ofthe GW 200 in the wireless communication system according to the fourthembodiment. FIG. 30 is a block diagram illustrating an exemplaryconfiguration of a delay measuring unit 236 of the GW 200 in thewireless communication system according to the fourth embodiment. In theGW 200 illustrated in FIG. 29, the OS/driver layer 230 includes thedelay measuring unit 236 in addition to having the configurationillustrated in FIG. 5. The delay measuring unit 236 includes a countercapture 2361, a delay measurement control unit 2362, a delay counter2363, and a delay packet data generating unit 2364.

The delay measurement control unit 2362 receives a delay measurementrequest and a delay measurement control timing from the user dataprocessing unit 241, and notifies the transmission-reception timingcontrol unit 235 about the delay measurement control timing. Accordingto the delay measurement control timing, the transmission-receptiontiming control unit 235 issues a delay measurement start notification tothe delay counter 2363. Then, the delay counter 2363 resets the countervalue to zero, and at the same time issues a data transmission requestto the delay packet data generating unit 2364. The delay packet datagenerating unit 2364 sends delay data to the transmission data buffer231, so that a delay measurement packet gets sent from the GW 200. Atthat time, in the GW 200, the counter capture 2361 captures thetransmission period of the delay measurement packet.

After sending the delay measurement packet, the GW 200 waits for theloop-back of the delay measurement packet. The delay measurement packetis sent from the GW 200 in the next slot to the AP 300 identified as “AP#1”, and is then sent from the AP 300 identified as “AP #1” in the nextslot to the STA 400. Moreover, the delay measurement packet is sent fromthe STA 400 in the next slot to the AP 300 identified as “AP #1”, and isthen sent from the AP 300 identified as “AP #1” in the next slot to theGW 200. In the GW 200, at the timing at which the reception data buffer233 receives the delay measurement packet, the counter capture 2361captures the reception period of the delay measurement packet. That is,the counter capture 2361 captures a delay counter value from thetransmission timing of the delay measurement packet to the receptiontiming of the delay measurement packet. The delay counter value is sentfrom the GW 200 to the STA 400 via the AP 300 identified as “AP #1”.

The transmission-reception timing control unit 435 of the STA 400 (FIG.7) calculates the advancement period of the uplink data based on thedelay counter value. Herein, T_(GW) represents the delay counter value(the delay measurement packet delay period) in the GW 200; T_(STA)represents the transmission-reception delay period in the STA 400; andT-Advance represents the advancement period of uplink data. In thiscase, the advancement period T-advance of uplink data is calculated asfollows.

T-Advance=T _(GW) −T _(STA)

The transmission-reception timing control unit 435 of the STA 400 (FIG.7) uses the calculated advancement period T-Advance and adjusts thetransmission timing of data reaching the GW 200 using multihopcommunication of the TDD type.

Issues

Generally, since each AP 300 and each STA 400 operates according to anasynchronous clock, the delay measurement value undergoes constantchanges. Hence, the delay measurement as described above needs to befrequently performed during the operations too. At the time ofperforming the delay measurement, if the target path is being accessedfrom elsewhere too, then there occurs an unintended delay in the delaymeasurement packet, and thus to perform the delay measurement isdifficult in an accurate way.

Solution

FIG. 31 is a diagram for explaining a solution to the issues arising inthe wireless communication system according to the fourth embodiment.Herein, the server 100 sends, to the GW 200, delay measurementinformation (described later) containing a delay measurement path P41from the GW 200 to the STA 400 identified as “STA #1” via the AP 300identified as “AP #1”. For example, the delay measurement information(described later) is transferred from the GW 200 to the STA 400identified as “STA #1” via the AP 300 identified “AP #1”, and istransferred from the GW 200 to the STAs 400 identified as “STA #2” and“STA #3” via the APs 300 identified “AP #2” and “AP #3”.

In this case, based on the delay measurement information (describedlater); the GW 200, the AP 300 identified as “AP #1”, and the STA 400identified as “STA #1” that are present in the delay measurement pathP41 transfer the delay measurement packet in the time periods of theCSMA type. Then, the GW 200 performs delay measurement for measuring thedelay period between the transmission of the delay measurement packetand the reception thereof in the delay measurement path P41. The delayperiod is equivalent to the delay counter value (the delay measurementpacket delay period) T_(GW) mentioned above. Based on the delay countervalue (the delay measurement packet delay period) T_(GW) notified fromthe GW 200, the STA 400 identified as “STA #1” calculates theadvancement period T-Advance meant for adjusting the timing of sendingthe uplink data using multihop communication of the TDD type. That is,the STA 400 identified as “STA #1” performs delay adjustment.

When delay measurement and delay adjustment is being performed, based onthe delay measurement information (described later), the wirelesscommunication devices not present in the delay measurement path P41 stopCSMA communication with the wireless communication devices present inthe delay measurement path P41 (refer to “transmission-receptiontermination paths” illustrated using dotted lines in FIG. 31). Forexample, the AP 300 identified as “AP #2” represents a wirelesscommunication device not present in the delay measurement path P41. Inthis case, based on the delay measurement information, the AP 300identified as “AP #2” stops CSMA communication with the GW 200 presentin the delay measurement path P41. Moreover, for example, the AP 300identified as “AP #3” represents a wireless communication device notpresent in the delay measurement path P41. In this case, based on thedelay measurement information, the AP 300 identified as “AP #3” stopsthe communication with the STA 400 identified as “STA #1”. With that,the abovementioned issues get resolved.

Herein, a wireless communication device not present in the delaymeasurement path P41 can perform CSMA communication with the otherwireless communication devices not present in the delay measurement pathP41 (refer to “CSMA-allowed paths” illustrated using dashed lines inFIG. 31). For example, when the AP 300 identified as “AP #2” representsa wireless communication device not present in the delay measurementpath P41, it performs CSMA communication with the AP 300 identified as“AP #3”. For example, when the AP 300 identified as “AP #3” represents awireless communication device not present in the delay measurement pathP41, it performs CSMA communication with the STAs 400 identified as “STA#2” and “STA #3”.

In this way, the server 100 decides the delay measurement schedule ofeach path as the delay measurement information (described later); andnotifies the GW 200, the APs 300, and the STAs 400 about the delaymeasurement information. The notification can include specification upto the hyper frame number, thereby enabling an advance notice ofsubstantially few tens of seconds. The delay measurement path P41 thatis set in the schedule (the delay measurement information) is treated asthe path to be used in the actual measurement, and the paths notaffecting the delay measurement (the paths other than the delaymeasurement path P41) are treated as the normal CSMA access paths.However, even in the paths other than the delay measurement path P41;the GW 200 and the APs 300 identified as “AP #2” and “AP #3” are notallowed to be accessed. Hence, the transmission-reception terminationpaths (refer to the dotted lines in FIG. 31) are set in the schedule(the delay measurement information). Then, the GW 200, the AP 300identified as “AP #1”, and the STA 400 identified as “STA #1” present inthe delay measurement path P41 transfer delay measurement packets basedon the schedule (the delay measurement information); and the GW 200performs delay measurement. The STA 400 identified as “STA #1”calculates the advancement period T-Advance based on the delay countervalue (the delay measurement packet delay period) T_(GW) notified fromthe GW 200. Then, the STA 400 identified as “STA #1” performs delayadjustment using the advancement period T-Advance, and the APs 300 andthe STAs 400 start the uplink access with the delay adjustment servingas the trigger.

The delay measurement is fundamentally performed in response to thereceipt of a probe request (a connection request) issued by the GW 200.Moreover, during the operations too, the delay measurement can beperformed at an arbitrary timing in response to a delay measurementrequest issued by the GW 200. In either case, the delay measurement isperformed in response to a start request from the server 100.

FIG. 32 is a sequence diagram illustrating an exemplary solution to theissues arising in the wireless communication system according to thefourth embodiment.

Firstly, in the wireless communication system according to the fourthembodiment, “delay measurement preparation” illustrated in FIG. 32 isperformed in the time periods of the TDD type.

The server 100 generates the delay measurement information according tothe schedule. The delay measurement information contains the STA number“STA #1” of the target STA 400, contains information about the delaymeasurement path P41, and contains the measurement start period at thetime of performing the delay measurement in the time periods of the CSMAtype. The information about the delay measurement path P41 contains theinformation about the transmission-reception termination paths (refer tothe dotted lines illustrated in FIG. 31) and the information about theCSMA-allowed paths (refer to dashed lines illustrated in FIG. 31). Then,the server 100 issues a delay measurement request, which includes thedelay measurement information, to the GW 200 (Step S400).

The GW 200 receives the delay measurement request from the server 100and adds the delay measurement information, which is included in thedelay measurement request, to the beacon information #0. Then, the GW200 sends the beacon information #0, which contains the delaymeasurement information, in the time period of the slot “SLOT #0” (StepS401).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the GW 200 receives the beacon information #0 that is sent from theGW 200 in the time period of the slot “SLOT #0” and that contains thedelay measurement information. Herein, the AP 300 identified as “AP #1”obtains the delay measurement information and recognizes that it itselfis present in the delay measurement path P41. Then, the AP 300identified as “AP #1” sends the beacon information #0, which containsthe delay measurement information, as the beacon information #1 in thetime period of the slot “SLOT #1” (Step S402).

The STA 400 identified as “STA #1” and representing the neighboring nodeto the AP 300 identified as “AP #1” receives the beacon information #1that is sent from the AP 300 identified as “AP #1” in the time period ofthe slot “SLOT #1” and that contains the delay measurement information.As a result of obtaining the delay measurement information, the STA 400identified as “STA #1” recognizes that it itself is present in the delaymeasurement path P41 (Step S403).

The GW 200 sends the beacon information #0, which contains the delaymeasurement information, in the time period of the slot “SLOT #0”. Atthat time, the frame monitoring control unit 243 of the GW 200 sets thedelay measurement information in the delay measuring unit 236 and thetransmission-reception timing control unit 235 (Step S404). When thedelay measurement information is set in the delay measuring unit 236 andthe transmission-reception timing control unit 235, the GW 200recognizes that the “delay measurement preparation” is complete.

Subsequently, in the wireless communication system according to thefourth embodiment, “delay measurement execution” illustrated in FIG. 32is performed in the time periods of the CSMA type specified in the“delay measurement preparation”.

The AP 300 identified as “AP #2” and representing the neighboring nodeto the GW 200 receives the beacon information #0 that is sent from theGW 200 in the time period of the slot “SLOT #0” and that contains thedelay measurement information. As a result of obtaining the delaymeasurement information, the AP 300 identified as “AP #2” recognizesthat it itself is not present in the delay measurement path P41. In thiscase, the AP 300 identified as “AP #2” switches to the standby state(Step S405). That is, the AP 300 identified as “AP #2” stops the CSMAcommunication with the GW 200 that is present in the delay measurementpath P41. Meanwhile, the AP 300 identified as “AP #2” can perform CSMAcommunication with the AP 300 identified as “AP #3”. In an identicalmanner, the AP 300 identified as “AP #3”, the STA 400 identified as “STA#2”, and the STA 400 identified as “STA #3” switch to the standby state.

The transmission-reception timing control unit 235 of the GW 200, whichis present in the delay measurement path P41, issues a delay measurementstart trigger to the delay measuring unit 236 at the measurement starttiming. Upon receiving the delay measurement start trigger, the delaymeasuring unit 236 resets the counter value of the delay counter 2363 tozero, and at the same time sends delay data to the transmission databuffer 231, so that the delay measurement packet gets sent from the GW200. That is, the GW 200 present in delay measurement path P41 sends thedelay measurement packet to the AP 300 identified as “AP #1” and presentin the delay measurement path P41. At that time, in the GW 200, thecounter capture 2361 captures the transmission period of the delaymeasurement packet. That is, the counter capture 2361 starts countingthe delay counter value (the delay measurement packet delay period)T_(GW) (Step S406). Herein, the contents of the delay measurement packetare not particularly defined.

The AP 300 identified as “AP #1” and present in the delay measurementpath P41 receives the delay measurement packet from the GW 200 and sendsit in the next slot to the STA 400 identified as “STA #1” and present inthe delay measurement path P41 (Step S407).

The STA 400 identified as “STA #1” and present in the delay measurementpath P41 receives the delay measurement packet from the AP 300identified as “AP #1”, and sends it in the next slot to the STA 300identified as “STA #1” and present in the delay measurement path P41(Step S408).

The AP 300 identified as “AP #1” and present in the delay measurementpath P41 sends the delay measurement packet in the next slot to the GW200 present in the delay measurement path P41 (Step S409).

In the GW 200 present in the delay measurement path P41, at the timingat which the reception data buffer 233 receives the delay measurementpacket, the counter capture 2361 captures the reception period of thedelay measurement packet. That is, the counter capture 2361 captures thedelay counter value (the delay measurement packet delay period) T_(GW)from the transmission timing to the reception timing of the delaymeasurement packet (Step S410).

The GW 200 present in the delay measurement path P41 sends, as the delaycounter value information packet, the packet including the informationabout the delay counter value T_(GW) to the AP 300 identified as “AP #1”and present in the delay measurement path P41 (Step S411).

The AP 300 identified as “AP #1” and present in the delay measurementpath P41 receives the delay counter value information packet from the GW200, and sends it in the next slot to the STA 400 identified as “STA #1”and present in the delay measurement path P41 (Step S412).

The STA 400 identified as “STA #1” and present in the delay measurementpath P41 receives the delay counter value information packet from the AP300 identified as “AP #1”. Based on the delay counter value T_(GW)included in the delay counter value information packet, thetransmission-reception timing control unit 435 of the STA 400 identifiedas “STA #1” calculates the advancement period T-Advance of the uplinkdata. Then, based on the calculated advancement period T-Advance, thetransmission-reception timing control unit 435 updates the transmissionstart position of the uplink data of the TDD technology (Step S413).

Meanwhile, after sending the delay counter value information packet tothe AP 300 identified as “AP #1” and present in the delay measurementpath P41, the GW 200 present in the delay measurement path P41 sends adelay measurement completion notification including the informationabout the delay counter value T_(GW) to the server 100 (Step S414). Whenthe delay measurement completion notification is received from the GW200, the server 100 recognizes that the “delay measurement execution” iscomplete.

Effect

As described above, in the wireless communication system according tothe fourth embodiment, the server 100 sends the delay measurementinformation that contains the delay measurement path P41 from a firstwireless communication device (in this case, the GW 200) to a secondwireless communication device (in this case, the STA 400 identified as“STA #1”) among a plurality of wireless communication devices (the GW200, the APs 300, and the STAs 400). In each wireless communicationdevice present in the delay measurement path P41 (in this case, the GW200, the AP 300 identified as “AP #1”, and the STA 400 identified as“STA #1”), the notification information processing unit transferspackets in the time periods of the CSMA type based on the delaymeasurement information.

For example, when the GW 200 represents the wireless communicationdevice, the notification information processing unit includes the analogprocessing layer 210, the media processing layer 220, the OS/driverlayer 230, and the application layer 240. Alternatively, for example,when the AP 300 represents the wireless communication device, thenotification information processing unit includes the analog processinglayer 310, the media processing layer 320, the OS/driver layer 330, andthe application layer 340. Still alternatively, for example, when theSTA 400 represents the wireless communication device, the notificationinformation processing unit includes the analog processing layer 410,the media processing layer 420, the OS/driver layer 430, and theapplication layer 440. For example, with reference to FIG. 31, when theGW 200 represents the wireless communication device and when thenotification information processing unit thereof receives the delaymeasurement information from the server 100, the notificationinformation processing unit transfers the delay measurement informationto the AP 300 identified as “AP #1”. For example, with reference to FIG.31, when the AP 300 identified as “AP #1” represents the wirelesscommunication device and when the notification information processingunit thereof receives the delay measurement information from the GW 200,the notification information processing unit transfers the delaymeasurement information to the STA 400 identified as “STA #1”.

Then, the notification information processing unit of the GW 200 (inthis case, the delay measuring unit 236) performs delay measurement formeasuring the delay period (the delay counter value T_(a)d from thetransmission of packets to the reception thereof in the delaymeasurement path P41. Based on the delay period (the delay counter valueT_(a)d notified from the GW 200, the notification information processingunit of the STA 400 identified as “STA #1” calculates the advancementperiod T-advance meant for adjusting the timing of sending data of theTDD type. That is, the STA 400 identified as “STA #1” performs delayadjustment.

While the delay measurement and the delay adjustment is being performed,the communication processing unit of the wireless communication devicesnot present in the delay measurement path P41 stop the CSMAcommunication with the wireless communication devices present in thedelay measurement path P41 based on the delay measurement information.For example, when the AP 300 represents the wireless communicationdevice not present in the delay measurement path P41, the notificationinformation processing unit includes the analog processing layer 310,the media processing layer 320, the OS/driver layer 330, and theapplication layer 340. For example, when the AP 300 identified as “AP#2” represents the wireless communication device not present in thedelay measurement path P41, the AP 300 identified as “AP #2” stops theCSMA communication with the GW 200, which is present in the delaymeasurement path P41, based on the delay measurement information. Forexample, when the AP 300 identified as “AP #3” represents the wirelesscommunication device not present in the delay measurement path P41, theAP 300 identified as “AP #3” stops the CSMA communication with the AP300 identified as “AP #1” and with the STA 400 identified as “STA #1”based on the delay measurement information.

In this way, in the wireless communication system according to thefourth embodiment, when the GW 200 performs delay measurement in thedelay measurement path P41, the wireless communication devices notpresent in the delay measurement path P41 stop the CSMA communicationwith the wireless communication devices present in the delay measurementpath P41. As a result, in the wireless communication system according tothe fourth embodiment, the GW 200 can perform delay measurement in anaccurate way.

[e] Fifth Embodiment

Issues

FIGS. 33 to 36 are diagrams for explaining the issues arising in thewireless communication system according to a fifth embodiment. Asillustrated in FIG. 33, each AP 300 fundamentally operates according toa free-running clock included therein (for example, refer to thefree-running clock 30 illustrated in FIG. 9). Hence, for example,between the AP 300 identified as “AP #n” and the AP 300 identified as“AP #m”, the frequency (in this case, the clock) becomes asynchronous.For that reason, there occurs a time lag between the AP 300 identifiedas “AP #n” and the AP 300 identified as “AP #m”. As a result, asillustrated in FIG. 34, between the AP 300 identified as “AP #n” and theAP 300 identified as “AP #m”, the slot positions become misaligned. Thatis, there occurs misalignment in the frame positions. In order tocorrect such misalignment, the delay adjustment needs to be frequentlyperformed in the time periods of the CSMA type. However, if the delayadjustment is frequently performed, the system happens to have lowfrequency usage efficiency.

For example, as illustrated in FIG. 35, the AP 300 receives the data(packets) sent from the GW 200, and then sends the packets in thespecified slot position to the STA 400. When there is no misalignment inthe slot positions due to asynchrony, the STA 400 can normally receivethe packets sent from the AP 300 in the specified slot. However, asillustrated in FIG. 36, when there is misalignment in the slot positionsbetween the AP 300 and the STA 400, it is difficult for the STA 400 tonormally receive the packets sent from the AP 300 in the specified slot.

Solution 1

Solution 1-1

FIG. 37 is a diagram for explaining a solution 1-1 with respect to theissues arising in the wireless communication system according to thefifth embodiment.

At the time of booting, each wireless communication device (the GW 200,the APs 300, and the STAs 400) compares the starting position “SLOT #0”of the frame “FRAME #n” in the free-running clock with the startingposition “SLOT #0” of the frame at the time of receiving beaconinformation. More particularly, the wireless communication device (forexample, the STA 400 identified as “STA #1”) detects a time differenceΔt_(FRAME) between the starting position “SLOT #0” of the frame “FRAME#n” in the free-running clock and the starting position “SLOT #0” of theframe at the time of receiving beacon information. Then, the wirelesscommunication device (the STA 400 identified as “STA #1”) determineswhether or not the time difference Δt_(FRAME) is equal to or greaterthan a threshold value.

If the time difference Δt_(FRAME) is equal to or greater than thethreshold value, then the wireless communication device (in this case,the STA 400 identified as “STA #1”) issues a resynchronization requestto the server 100. In response to the resynchronization request, theserver 100 sends delay measurement information as a resynchronizationinstruction. Using the delay measurement information, the wirelesscommunication devices present in the delay measurement path P41 (in thiscase, the GW 200, the AP 300 identified as “AP #1”, and the STA 400identified as “STA #1”) are specified; and delay measurement and delayadjustment is performed. Based on the delay measurement and the delayadjustment, each wireless communication device present in the delaymeasurement path P41 (i.e., the GW 200, the AP 300 identified as “AP#1”, and the STA 400 identified as “STA #1”) synchronizes thecorresponding frame “FRAME #n” in the free-running clock to the frame atthe time of receiving beacon information. With that, the abovementionedissues get resolved.

FIG. 38 is a block diagram illustrating an exemplary configuration ofthe transmission-reception timing control unit 35 of the GW 200, the APs300, and the STAs 400 in the wireless communication system according tothe fifth embodiment. The transmission-reception timing control unit 35includes a frame start comparing unit 3506 in addition to having theconfiguration illustrated in FIG. 9 or FIG. 10.

The transmission-reception timing control unit 35 monitors the timedifference Δt_(FRAME). That is, the frame start comparing unit 3506 ofthe transmission-reception timing control unit 35 obtains, as thestarting position “SLOT #0” of the frame at the time of receiving beaconinformation, the starting position “SLOT #0” of the frame obtained fromthe counter clear timing generating unit 3502. Moreover, the frame startcomparing unit 3506 obtains, as the start position “SLOT #0” of theframe “FRAME #n” in the free-running clock 30, the starting position“SLOT #0” of the frame generated by the transmission-reception timingdeciding unit 3504 using the counter value. Then, the frame startcomparing unit 3506 compares the start position “SLOT #0” of the frame“FRAME #n” in the free-running clock and the starting position “SLOT #0”of the frame at the time of receiving beacon information. If the resultof comparison indicates that the time difference Δt_(FRAME) is equal toor greater than the threshold value, then the frame start comparing unit3506 notifies the frame monitoring control unit 43 about the same viathe transmission-reception timing deciding unit 3504. In this case, theframe monitoring control unit 43 issues a frame resynchronizationrequest to the server 100; and the resynchronization request is outputfrom the transmission data buffer 31 via the transmission-receptiontiming deciding unit 3504.

FIG. 39 is a sequence diagram illustrating an exemplary solution 1-1with respect to the issues arising in the wireless communication systemaccording to the fifth embodiment. With reference to FIG. 39, theexplanation is given for the case in which the STA 400 identified as“STA #1” detects the time difference Δt_(FRAME) between the startingposition “SLOT #0” of the frame “FRAME #n” in the free-running clock 30and the starting position “SLOT #0” of the frame at the time ofreceiving beacon information.

For example, in the time periods of the TDD type, the GW 200 sendsbeacon information (Step S500).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the GW 200 receives the beacon information sent from the GW 200, andthen sends the beacon information (Step S501).

The STA 400 identified as “STA #1” and representing the neighboring nodeto the AP 300 identified as “AP #1” receives the beacon information sentfrom the AP 300 identified as “AP #1”. Then, the STA 400 identified as“STA #1” detects the time difference Δt_(FRAME) between the startingposition “SLOT #0” of the frame “FRAME #n” in the free-running clock 30and the starting position “SLOT #0” of the frame at the time ofreceiving beacon information. That is, according to the time differenceΔt_(FRAME), the STA 400 identified as “STA #1” detects the misalignmentin the starting positions of the frames (Step S502).

If the time difference Δt_(FRAME) is equal to or greater than thethreshold value, then the STA 400 identified as “STA #1” issues a frameresynchronization request packet as a resynchronization request, andthen sends the frame resynchronization request packet (Step S503).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the STA 400 identified as “STA #1” performs packet bridgetransmission with respect to the frame resynchronization packet sentfrom the STA 400 identified as “STA #1”. That is, the AP 300 identifiedas “AP #1” receives the frame resynchronization request packet sent fromthe STA 400 identified as “STA #1”, and sends the frameresynchronization request packet (Step S504).

The GW 200 representing the neighboring node to the AP 300 identified as“AP #1” performs packet bridge transmission with respect to the frameresynchronization packet sent from the AP 300 identified as “AP #1”.That is, the GW 200 receives the frame resynchronization request packetsent from the AP 300 identified as “AP #1”, and then sends the frameresynchronization request packet to the server 100 (Step S505).

The server 100 receives the frame resynchronization request packet sentfrom the GW 200. At that time, in the time periods of the TDD type,delay measurement preparation is performed with respect to the targetSTA (in this case, the STA 400 identified as “STA #1” (Step S506). Then,in the time periods of the CSMA type, delay measurement execution isperformed with respect to the target STA (in this case, the STA 400identified as “STA #1” (Step S507). Herein, delay measurementpreparation (Step S506) is equivalent to “delay measurement preparation”illustrated in FIG. 32, and delay measurement execution (Step S507) isequivalent to “delay measurement execution” illustrated in FIG. 32.

Solution 1-2

FIG. 40 is a diagram for explaining a solution 1-2 with respect to theissues arising in the wireless communication system according to thefifth embodiment.

At the time of booting, each wireless communication device (the GW 200,the APs 300, and the STAs 400) compares the starting position “SLOT #0”of the frame “FRAME #n” in the free-running clock 30 with the startingposition “SLOT #0” of the frame at the time of receiving beaconinformation. More particularly, the wireless communication device (forexample, the STA 400 identified as “STA #1”) detects the time differenceΔt_(FRAME) between the starting position “SLOT #0” of the frame “FRAME#n” in the free-running clock 30 and the starting position “SLOT #0” ofthe frame at the time of receiving beacon information. Then, thewireless communication device (the STA 400 identified as “STA #1”)determines whether or not the time difference Δt_(FRAME) is equal to orgreater than a threshold value.

If the time difference Δt_(FRAME) is equal to or greater than thethreshold value, then the wireless communication device (in this case,the STA 400 identified as “STA #1”) adjusts the slot length of thestarting position “SLOT #0” of the frame “FRAME #n” in the free-runningclock 30 based on the time difference Δt_(FRAME). With that, thewireless communication device (the STA 400 identified as “STA #1”)synchronizes the frame “FRAME #n” in the free-running clock 30 to theframe at the time of receiving beacon information. That is, based on thetime difference Δt_(FRAME), the frame start comparing unit 3506 of thewireless communication device (STA 400 identified as “STA #1”)autonomously clears the counter value of the counter 3503 illustrated inFIG. 38, and synchronizes the frames. With that, the abovementionedissues get resolved.

FIG. 41 is a sequence diagram illustrating an exemplary solution 1-2with respect to the issues arising in the wireless communication systemaccording to the fifth embodiment. With reference to FIG. 41, theexplanation is given for the case in which the STA 400 identified as“STA #1” detects the time difference Δt_(FRAME) between the startingposition “SLOT #0” of the frame “FRAME #n” in the free-running clock 30and the starting position “SLOT #0” of the frame at the time ofreceiving beacon information.

For example, in the time periods of the TDD type, the GW 200 sendsbeacon information (Step S600).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the GW 200 receives the beacon information sent from the GW 200, andthen sends the beacon information (Step S601).

The STA 400 identified as “STA #1” and representing the neighboring nodeto the AP 300 identified as “AP #1” receives the beacon information sentfrom the AP 300 identified as “AP #1”. Then, the STA 400 identified as“STA #1” detects the time difference Δt_(FRAME) between the startingposition “SLOT #0” of the frame “FRAME #n” in the free-running clock 30and the starting position “SLOT #0” of the frame at the time ofreceiving beacon information. That is, according to the time differenceΔt_(FRAME), the STA 400 identified as “STA #1” detects the misalignmentin the starting positions of the frames (Step S602).

If the time difference Δt_(FRAME) is equal to or greater than thethreshold value, then the STA 400 identified as “STA #1” adjusts, basedon the time difference Δt_(FRAME), the slot length of the startingposition “SLOT #0” of the frame “FRAME #n” in the free-running clock 30.In this case, based on the time difference Δt_(FRAME), the STA 400identified as “STA #1” autonomously clears the counter value of thecounter 3503 illustrated in FIG. 38, and synchronizes the frames (StepS603). As a result, the STA device identified as “STA #1” synchronizesthe frame “FRAME #n” in the free-running clock 30 to the frame at thetime of receiving beacon information.

The STA 400 identified as “STA #1” issues a frame resynchronizationcompletion packet indicating that the frames have been synchronized, andsends the frame resynchronization completion packet (Step S604).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the STA 400 identified as “STA #1” performs packet bridgetransmission with respect to the frame resynchronization completionpacket. That is, the AP 300 identified as “AP #1” receives the frameresynchronization completion packet sent from the STA 400 identified as“STA #1”, and then sends the frame resynchronization completion packet(Step S605).

The GW 200 representing the neighboring node to the AP 300 identified as“AP #1” performs packet bridge transmission with respect to the frameresynchronization completion packet sent from the AP 300 identified as“AP #1”. That is, the GW 200 receives the frame resynchronizationcompletion packet from the AP 300 identified as “AP #1”, and sends it tothe server 100 (Step S606).

Meanwhile, in the solution 1-2 in which frame resynchronization isautonomously performed, the resynchronization period is shorter ascompared to the solution 1-1 in which frame resynchronization issystemically performed. On the other hand, in the solution 1-2, there isa possibility that autonomous frame resynchronization occurs chronicallyin the wireless communication devices (the GW 200, the APs 300, and theSTAs 400) thereby likely causing deterioration in the networkperformance. Hence, it is desirable to implement the solution 1-1.

Solution 2

The wireless communication devices (the GW 200, the APs 300, and theSTAs 400) monitor whether or not data can be normally received from thespecified slots.

When to receive the packets (data) from the specified slot normally isdifficult, the wireless communication devices (the GW 200, the APs 300,and the STAs 400) notify the server 100 about a resynchronizationrequest indicating that the packets are not normally received. Inresponse to the resynchronization request, the server 100 sends delaymeasurement information as a resynchronization instruction. Using thedelay measurement information, the wireless communication devicespresent in the delay measurement path P41 (in this case, the GW 200, theAP 300 identified as “AP #1”, and the STA 400 identified as “STA #1”)are specified; and delay measurement and delay adjustment is performed.Based on the delay measurement and the delay adjustment, each wirelesscommunication device present in the delay measurement path P41 (i.e.,the GW 200, the AP 300 identified as “AP #1”, and the STA 400 identifiedas “STA #1”) synchronizes the corresponding frame “FRAME #n” in thefree-running clock to the frame at the time of receiving beaconinformation. With that, the abovementioned issues get resolved.

The transmission-reception timing control unit 35 illustrated in FIG. 38monitors the specified slot. The transmission-reception timing decidingunit 3504 notifies the packet extracting unit 22 about reception periodend information at the end of the reception period. At that time, if itis detected that the packet extracting unit 22 is still receiving data,then the transmission-reception timing deciding unit 3504 issues anout-of-reception-range error notification to the frame monitoringcontrol unit 43, and destroys the reception packets. At the same time,the frame monitoring control unit 43 issues a frame resynchronizationrequest to the server 100; and the resynchronization request is outputfrom the transmission data buffer 31 via the transmission-receptiontiming deciding unit 3504.

FIG. 42 is a sequence diagram illustrating an example of a solution 2with respect to the issues arising in the wireless communication systemaccording to the fifth embodiment. With reference to FIG. 42, theexplanation is given about the case in which the STA identified as “STA#1” does not normally receive the packets (data) from the specifiedslot.

For example, in the time periods of the TDD type, the server 100 sendsuser data (hereinafter, referred to as a user data packet) (Step S700).

The GW 200 performs packet bridge transmission with respect to the userdata packet sent from the server 100. That is, the GW 200 receives theuser data packet sent from the server 100, and then sends the user datapacket (Step S701).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the GW 200 performs packet bridge transmission with respect to theuser data packet sent from the GW 200. That is, the AP identified as “AP#1” receives the user data packet sent from the GW 200, and then sendsthe user data packet (Step S702).

The STA 400 identified as “STA #1” and representing the neighboring nodeto the AP 300 identified as “AP #1” monitors whether or not the userdata packet sent from the AP 300 identified as “AP #1” is normallyreceivable from the specified slot. Herein, if the user data packet isnot normally received from the specified slot, the STA 400 identified as“STA #1” detects an out-of-reception-range error (Step S703).

If an out-of-reception-range error is detected, the STA 400 identifiedas STA #1 issues a frame resynchronization request packet as aresynchronization request mentioned earlier, and sends the frameresynchronization request packet (Step S704).

The AP 300 identified as “AP #1” and representing the neighboring nodeto the STA 400 identified as “STA #1” performs packet bridgetransmission with respect to the frame resynchronization request packetsent from the STA 400 identified as “STA #1”. That is, the AP 300identified as “AP #1” receives the frame resynchronization requestpacket sent from the STA 400 identified as “STA #1”, and then sends theframe resynchronization request packet (Step S705).

The GW 200 representing the neighboring node to the AP 300 identified as“AP #1” performs packet bridge transmission with respect to the frameresynchronization request packet sent from the AP 300 identified as “AP#1”. That is, the GW 200 receives the frame resynchronization requestpacket sent from the AP 300 identified as “AP #1”, and then sends theframe resynchronization request packet to the server 100 (Step S706).

The server 100 receives the frame resynchronization request packet sentfrom the GW 200. At that time, in the time periods of the TDD type,delay measurement preparation is performed with respect to the targetSTA (in this case, the STA 400 illustrated as “STA #1”) (Step S707).Then, in the time periods of the CSMA type specified in the delaymeasurement preparation, delay measurement execution is performed withrespect to the target STA (the STA 400 identified as “STA #1”) (StepS708). Herein, delay measurement preparation (Step S707) is equivalentto “delay measurement preparation” illustrated in FIG. 32, and delaymeasurement execution (Step S708) is equivalent to “delay measurementexecution” illustrated in FIG. 32.

Effect

As described above, in the wireless communication system according tothe fifth embodiment, the following effect can be achieved because ofthe solution 1-1, the solution 1-2, and the solution 2 with respect tothe issues.

Firstly, in the solution 1-1, the notification information processingunit of each of a plurality of wireless communication devices obtainsthe starting position “SLOT #0” of the frame “FRAME #n” in thefree-running clock 30 and obtains the starting position “SLOT #0” of theframe at the time of receiving beacon information. Then, thenotification information processing unit detects the time differenceΔt_(FRAME) between the starting position “SLOT #0” of the frame “FRAME#n” in the free-running clock 30 and the starting position “SLOT #0” ofthe frame at the time of receiving beacon information. If the timedifference Δt_(FRAME) is equal to or greater than a threshold value,then the notification information processing unit issues aresynchronization request to the server 100.

In the solution 1-1, for example, if the GW 200 represents the wirelesscommunication device, then the notification processing unit includes theanalog processing layer 210, the media processing layer 220, theOS/driver layer 230, and the application layer 240. Alternatively, forexample, if the AP 300 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 310, the media processing layer 320, the OS/driverlayer 330, and the application layer 340. Still alternatively, forexample, if the STA 400 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 410, the media processing layer 420, the OS/driverlayer 430, and the application layer 440. For example, with reference toFIG. 39, the STA 400 identified as “STA #1” represents the wirelesscommunication device and, when the detected time difference Δt_(FRAME)is equal to or greater than the threshold value, the notificationinformation processing unit issues a resynchronization request to theserver 100.

In response to the resynchronization request, the server 100 sends delaymeasurement information as a resynchronization instruction. Using thedelay measurement information, the wireless communication devicespresent in the delay measurement path P41 (in this case, the GW 200, theAP 300 identified as “AP #1”, and the STA 400 identified as “STA #1”)are specified; and delay measurement and delay adjustment is performed.Based on the delay measurement and the delay adjustment, each wirelesscommunication device present in the delay measurement path P41 (i.e.,the GW 200, the AP 300 identified as “AP #1”, and the STA 400 identifiedas “STA #1”) synchronizes the corresponding frame “FRAME #n” in thefree-running clock 30 to the frame at the time of receiving beaconinformation.

In this way, because of the solution 1-1 with respect to the issuesarising in the wireless communication system according to the fifthembodiment, delay adjustment can be performed on a periodic basiswithout having to frequently perform delay adjustment in the timeperiods of the CSMA type.

In the solution 1-2, the notification information processing unit ofeach of a plurality of wireless communication devices obtains thestarting position “SLOT #0” of the frame “FRAME #n” in the free-runningclock 30 and obtains the starting position “SLOT #0” of the frame at thetime of receiving beacon information. Then, the notification informationprocessing unit detects the time difference Δt_(FRAME) between thestarting position “SLOT #0” of the frame “FRAME #n” in the free-runningclock 30 and the starting position “SLOT #0” of the frame at the time ofreceiving beacon information. If the time difference Δt_(FRAME) is equalto or greater than a threshold value, then the notification informationprocessing unit adjusts the slot length of the starting position “SLOT#0” of the frame “FRAME #n” in the free-running clock 30 based on thetime difference Δt_(FRAME). With that, the notification informationprocessing unit synchronizes the corresponding frame “FRAME #n” in thefree-running clock 30 to the frame at the time of receiving beaconinformation.

In the solution 1-2, for example, if the GW 200 represents the wirelesscommunication device, then the notification processing unit includes theanalog processing layer 210, the media processing layer 220, theOS/driver layer 230, and the application layer 240. Alternatively, forexample, if the AP 300 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 310, the media processing layer 320, the OS/driverlayer 330, and the application layer 340. Still alternatively, forexample, if the STA 400 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 410, the media processing layer 420, the OS/driverlayer 430, and the application layer 440. For example, with reference toFIG. 41, the STA 400 identified as “STA #1” represents the wirelesscommunication device and, when the detected time difference Δt_(FRAME)is equal to or greater than the threshold value, the notificationinformation processing unit autonomously performs frameresynchronization based on the time difference Δt_(FRAME).

In this way, because of the solution 1-2 with respect to the issuesarising in the wireless communication system according to the fifthembodiment, delay adjustment can be performed on a periodic basiswithout having to frequently perform delay adjustment in the timeperiods of the CSMA type.

In the solution 2, firstly, if the data is not normally received fromthe specified slot, then the notification information processing unit ofeach of a plurality of wireless communication devices issues aresynchronization request to the server 100.

In the solution 2, for example, if the GW 200 represents the wirelesscommunication device, then the notification processing unit includes theanalog processing layer 210, the media processing layer 220, theOS/driver layer 230, and the application layer 240. Alternatively, forexample, if the AP 300 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 310, the media processing layer 320, the OS/driverlayer 330, and the application layer 340. Still alternatively, forexample, if the STA 400 represents the wireless communication device,then the notification information processing unit includes the analogprocessing layer 410, the media processing layer 420, the OS/driverlayer 430, and the application layer 440. For example, with reference toFIG. 42, the STA 400 identified as “STA #1” represents the wirelesscommunication device and, when the data is not normally received fromthe specified slot, the notification information processing unit issuesa resynchronization request to the server 100.

In response to the resynchronization request, the server 100 sends delaymeasurement information as a resynchronization instruction. Using thedelay measurement information, the wireless communication devicespresent in the delay measurement path P41 (in this case, the GW 200, theAP 300 identified as “AP #1”, and the STA 400 identified as “STA #1”)are specified; and delay measurement and delay adjustment is performed.Based on the delay measurement and the delay adjustment, each wirelesscommunication device present in the delay measurement path P41 (i.e.,the GW 200, the AP 300 identified as “AP #1”, and the STA 400 identifiedas “STA #1”) synchronizes the corresponding frame “FRAME #n” in thefree-running clock 30 to the frame at the time of receiving beaconinformation.

In this way, because of the solution 2 with respect to the issuesarising in the wireless communication system according to the fifthembodiment, delay adjustment can be performed on a periodic basiswithout having to frequently perform delay adjustment in the timeperiods of the CSMA type.

Other Embodiments

Meanwhile, in the first to fifth embodiments described above, theconstituent elements of the devices illustrated in the drawings aremerely conceptual, and need not be physically configured as illustrated.That is, the specific configurations of the constituent elements are notlimited to the illustrated configurations and the constituent elements,as a whole or in part, can be separated or integrated eitherfunctionally or physically based on various types of loads or usecondition.

Moreover, the various operations performed in the devices can beentirely or partially implemented in a central processing unit (CPU) (orin microcomputer such as a micro processing unit (MPU)) or a microcontroller unit (MCU). Alternatively, the various operations can beentirely or partially implemented in computer programs analyzed andexecuted in a CPU (or a microcomputer such as an MPU or an MCU), or canbe entirely or partially implemented using hardware such as wired logic.

The server 100, the GW 200, the APs 300, and the STAs 400 according tothe first to fifth embodiments can be implemented using, for example, ahardware configuration as described below.

FIG. 43 is a diagram illustrating an exemplary hardware configuration ofthe server 100. As illustrated in FIG. 43, the server 100 includes aprocessor 1001, a memory 1002, and an analog circuit 1003. Examples ofthe processor 1001 include a CPU, a digital signal processor (DSP), anda field programmable gate array (FPGA). Examples of the memory 1002include a random access memory (RAM) such as a synchronous dynamicrandom access memory (SDRAM); a read only memory (ROM); and a flashmemory.

The various operations performed in the server 100 according to thefirst to fifth embodiments can be implemented by making a processorexecute computer programs stored in various memories such as nonvolatilememory media. For example, computer programs corresponding to theoperations performed in the media processing layer 110, the applicationlayer 120, and the database layer 130 can be recorded in the memory1002, and the processor 1001 can execute those computer programs.

Herein, although it is assumed that the various operations performed inthe server 100 according to the first to fifth embodiments areimplemented by a single processor 1001, that is not the only possiblecase. Alternatively, the various operations can be implemented using aplurality of processors.

FIG. 44 is a diagram illustrating an exemplary hardware configuration ofthe GW 200. As illustrated in FIG. 44, the GW 200 includes a processor2001, a memory 2002, and an analog circuit 2003. Examples of theprocessor 2001 include a CPU, a DSP, and an FPGA. Examples of the memory2002 include a RAM such as an SDRAM; a ROM; and a flash memory.

The various operations performed in the GW 200 according to the first tofifth embodiments can be implemented by making a processor executecomputer programs stored in various memories such as nonvolatile memorymedia. For example, computer programs corresponding to the operationsperformed in the media processing layer 220, the OS/driver layer 230,and the application layer 240 can be recorded in the memory 2002; andthe processor 2001 can execute those computer programs. Meanwhile, theanalog processing layer 210 of the GW 200 illustrated in FIG. 5 isimplemented using the analog circuit 2003.

Herein, although it is assumed that the various operations performed inthe GW 200 according to the first to fifth embodiments are implementedby a single processor 2001, that is not the only possible case.Alternatively, the various operations can be implemented using aplurality of processors.

FIG. 45 is a diagram illustrating an exemplary hardware configuration ofthe AP 300. As illustrated in FIG. 45, the AP 300 includes a processor3001, a memory 3002, and an analog circuit 3003. Examples of theprocessor 3001 include a CPU, DSP, and an FPGA. Examples of the memory3002 include a RAM such as an SDRAM; a ROM; and a flash memory.

The various operations performed in the AP 300 according to the first tofifth embodiments can be implemented by making a processor executecomputer programs stored in various memories such as nonvolatile memorymedia. For example, computer programs corresponding to the operationsperformed in the media processing layer 320, the OS/driver layer 330,and the application layer 340 can be recorded in the memory 3002; andthe processor 3001 can execute those computer programs. Meanwhile, theanalog processing layer 310 of the AP 300 illustrated in FIG. 6 isimplemented using the analog circuit 3003.

Herein, although it is assumed that the various operations performed inthe AP 300 according to the first to fifth embodiments are implementedby a single processor 3001, that is not the only possible case.Alternatively, the various operations can be implemented using aplurality of processors.

FIG. 46 is a diagram illustrating an exemplary hardware configuration ofthe STA 400. As illustrated in FIG. 46, the STA 400 includes a processor4001, a memory 4002, and an analog circuit 4003. Examples of theprocessor 4001 include a CPU, DSP, and an FPGA. Examples of the memory4002 include a RAM such as an SDRAM; a ROM; and a flash memory.

The various operations performed in the STA 400 according to the firstto fifth embodiments can be implemented by making a processor executecomputer programs stored in various memories such as nonvolatile memorymedia. For example, computer programs corresponding to the operationsperformed in the media processing layer 420, the OS/driver layer 430,and the application layer 440 can be recorded in the memory 4002; andthe processor 4001 can execute those computer programs. Meanwhile, theanalog processing layer 410 of the STA 400 illustrated in FIG. 7 isimplemented using the analog circuit 4003.

Herein, although it is assumed that the various operations performed inthe STA 400 according to the first to fifth embodiments are implementedby a single processor 4001, that is not the only possible case.Alternatively, the various operations can be implemented using aplurality of processors.

As an aspect, the gap periods can be used in an effective manner.

All examples and conditional language recited herein are intended forpedagogical purposes of aiding the reader in understanding the inventionand the concepts contributed by the inventor to further the art, and arenot to be construed as limitations to such specifically recited examplesand conditions, nor does the organization of such examples in thespecification relate to a showing of the superiority and inferiority ofthe invention. Although the embodiments of the present invention havebeen described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A wireless communication system comprising: aserver that sends notification information in which starting position ofa frame is specified; and a plurality of wireless communication devicesrepresenting nodes assigned to the server, wherein each of the pluralityof wireless communication devices includes a notification informationprocessing unit that receives the notification information, and acommunication processing unit that, according to the notificationinformation, performs communication of time division duplex (TDD) type,and performs communication of carrier sense multiple access (CSMA) typeduring a period of time between a downlink time period and an uplinktime period of the TDD type.
 2. The wireless communication systemaccording to claim 1, wherein the notification information is assignedto a first slot among a plurality of slots assigned to a single frame,and in a plurality of paths in which the notification information istransferred, the notification information processing unit of theplurality of wireless communication devices assigns the notificationinformation to a slot, among the plurality of slots, that is present atposition corresponding to a node hop count indicating number of nodeswhich the notification information has passed through.
 3. The wirelesscommunication system according to claim 2, wherein the notificationinformation processing unit of the plurality of wireless communicationdevices assigns, in a first path among the plurality of paths in whichthe node hop count is identical, the notification information to a slot,among the plurality of slots, that is present at position correspondingto the node hop count, and copies the notification information in otherpaths other than the first path among the plurality of paths in whichthe node hop count is identical, and assigns the copied notificationinformation to a slot, among the plurality of slots, that is present atposition specified by the server.
 4. The wireless communication systemaccording to claim 1, wherein the server sends delay measurementinformation that contains a delay measurement path from a first wirelesscommunication device to a second wireless communication device among theplurality of wireless communication devices, the notificationinformation processing unit of each wireless communication devicepresent in the delay measurement path transfers a packet in the timeperiod of the CSMA type based on the delay measurement information, thenotification information processing unit of the first wirelesscommunication device performs delay measurement meant for measuringdelay period between transmission of the packet and reception of thepacket in the delay measurement path, the notification informationprocessing unit of the second wireless communication device performsdelay adjustment, which is meant for adjusting time of sending data ofthe TDD type, based on the delay period notified from the first wirelesscommunication device, and when the delay measurement and the delayadjustment is being performed, based on the delay measurementinformation, the communication processing unit of each wirelesscommunication device not present in the delay measurement path stopscommunication of the CSMA type with wireless communication devicespresent in the delay measurement path.
 5. The wireless communicationsystem according to claim 4, wherein when time difference betweenstarting position of frame in a free-running clock and starting positionof frame at time of receiving the notification information is equal toor greater than a threshold value, the notification informationprocessing unit of the plurality of wireless communication devicesissues a resynchronization request to the server, in response to theresynchronization request, the server sends the delay measurementinformation as a resynchronization instruction, and based on the delaymeasurement and the delay adjustment performed using the delaymeasurement information, the notification information processing unit ofeach wireless communication device present in the delay measurement pathspecified in the delay measurement information synchronizes frame in thefree-running clock to frame at time of receiving the notificationinformation.
 6. The wireless communication system according to claim 4,wherein when data is not normally receivable from a specified slot, thenotification information processing unit of the plurality of wirelesscommunication devices issues a resynchronization request to the server,in response to the resynchronization request, the server sends the delaymeasurement information as a resynchronization instruction, and based onthe delay measurement and the delay adjustment, the notificationinformation processing unit of each wireless communication devicepresent in the delay measurement path specified in the delay measurementinformation synchronizes frame in the free-running clock to frame attime of receiving the notification information.
 7. The wirelesscommunication system according to claim 1, wherein, when time differencebetween starting position of frame in free-running clock and startingposition of frame at time of receiving notification information is equalto or greater than a threshold value, the notification informationprocessing unit of the plurality of wireless communication devicessynchronizes frame in the free-running clock to frame at time ofreceiving the notification information by adjusting slot length ofstarting position of frame in the free-running clock based on the timedifference.
 8. A wireless communication device that represents a nodeassigned to a server which sends notification information meant forspecifying starting position of frame, the wireless communication devicecomprising: a notification information processing unit that receivesnotification information; and a communication processing unit that,according to the notification information, performs communication oftime division duplex (TDD) type, and performs communication of carriersense multiple access (CSMA) type during a period of time between adownlink time period and an uplink time period of the TDD type.
 9. Acommunication method in which a plurality of wireless communicationdevices representing nodes assigned to a server which sends notificationinformation meant for specifying starting position of frame, thecommunication method comprising: receiving the notification information;performing, according to the notification information, communication oftime division duplex (TDD) type; and performing communication of carriersense multiple access (CSMA) type during a period of time between adownlink time period and an uplink time period of the TDD type.